resolves #4623 

Also adds basic `flow` to webpack.js and the plugins.

This makes sure plugins like @zeit/next-typescript or @zeit/next-mdx don't have to provide the `hot-self-accept-loader`.
This fixes for example @zeit/next-mdx, which doesn't implement `pageExtensions` but we do use mdx as top level pages for https://github.com/zeit/docs

I have updated [examples/with-markdown](https://github.com/zeit/next.js/tree/canary/examples/with-markdown) in order to make it works with next 6 🎉 

<details>
<summary>Error</summary>
Error: Plugin/Preset files are not allowed to export objects, only functions. In /Users/zhenyatelegin/Desktop/next.js/examples/with-markdown/node_modules/markdown-in-js/babel.js
</details>

Hello!

I have updated `babel-plugin-module-resolver` to `^3.1.1` and moved it to `devDependencies` in [with-absolute-imports](https://github.com/zeit/next.js/tree/canary/examples/with-absolute-imports) example to make it work with Babel 7 :)

## Error logs
```
zhenyatelegin@MBP-Zhenya  ~/Desktop/next.js/examples/with-absolute-imports   canary  yarn build
yarn run v1.5.1
warning package.json: No license field
$ next build
> Failed to build
{ Error: (client) ./pages/index.js
Module build failed: Error: Cannot find module 'babel-plugin-module-resolver' from '/Users/zhenyatelegin/Desktop/next.js/examples/with-absolute-imports'
    at Function.module.exports [as sync] (/Users/zhenyatelegin/Desktop/next.js/node_modules/resolve/lib/sync.js:40:15)
    at resolveStandardizedName (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:78:29)
    at resolvePlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:27:10)
    at loadPlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:35:18)
    at createDescriptor (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:152:21)
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:104:12
    at Array.map (<anonymous>)
    at createDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:103:27)
    at createPluginDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:99:10)
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:50:19
    at plugins (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:40:25)
    at mergeChainOpts (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:296:68)
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:251:7
    at buildRootChain (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:85:20)
    at loadPrivatePartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:41:53)
    at Object.loadPartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:66:16)
 @ multi ./pages/index.js
    at /Users/zhenyatelegin/Desktop/next.js/dist/server/build/index.js:144:31
    at runWithDependencies (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/MultiCompiler.js:154:4)
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/async/dist/async.js:1140:9
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/async/dist/async.js:473:16
    at iteratorCallback (/Users/zhenyatelegin/Desktop/next.js/node_modules/async/dist/async.js:1064:13)
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/async/dist/async.js:969:16
    at /Users/zhenyatelegin/Desktop/next.js/node_modules/async/dist/async.js:1137:13
    at runCompilers (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/MultiCompiler.js:96:47)
    at fn (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/MultiCompiler.js:101:6)
    at compiler.run (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/MultiCompiler.js:150:5)
    at emitRecords.err (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/Compiler.js:265:13)
    at Compiler.emitRecords (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/Compiler.js:371:38)
    at emitAssets.err (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/Compiler.js:258:10)
    at applyPluginsAsyncSeries1.err (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/Compiler.js:364:12)
    at next (/Users/zhenyatelegin/Desktop/next.js/node_modules/tapable/lib/Tapable.js:218:11)
    at Compiler.compiler.plugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/webpack/lib/performance/SizeLimitsPlugin.js:99:4)
  errors:
   [ '(client) ./pages/index.js\nModule build failed: Error: Cannot find module \'babel-plugin-module-resolver\' from \'/Users/zhenyatelegin/Desktop/next.js/examples/with-absolute-imports\'\n    at Function.module.exports [as sync] (/Users/zhenyatelegin/Desktop/next.js/node_modules/resolve/lib/sync.js:40:15)\n    at resolveStandardizedName (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:78:29)\n    at resolvePlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:27:10)\n    at loadPlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:35:18)\n    at createDescriptor (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:152:21)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:104:12\n    at Array.map (<anonymous>)\n    at createDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:103:27)\n    at createPluginDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:99:10)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:50:19\n    at plugins (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:40:25)\n    at mergeChainOpts (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:296:68)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:251:7\n    at buildRootChain (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:85:20)\n    at loadPrivatePartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:41:53)\n    at Object.loadPartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:66:16)\n @ multi ./pages/index.js',
     '(server) ./pages/index.js\nModule build failed: Error: Cannot find module \'babel-plugin-module-resolver\' from \'/Users/zhenyatelegin/Desktop/next.js/examples/with-absolute-imports\'\n    at Function.module.exports [as sync] (/Users/zhenyatelegin/Desktop/next.js/node_modules/resolve/lib/sync.js:40:15)\n    at resolveStandardizedName (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:78:29)\n    at resolvePlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:27:10)\n    at loadPlugin (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/files/plugins.js:35:18)\n    at createDescriptor (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:152:21)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:104:12\n    at Array.map (<anonymous>)\n    at createDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:103:27)\n    at createPluginDescriptors (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:99:10)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:50:19\n    at plugins (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-descriptors.js:40:25)\n    at mergeChainOpts (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:296:68)\n    at /Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:251:7\n    at buildRootChain (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/config-chain.js:85:20)\n    at loadPrivatePartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:41:53)\n    at Object.loadPartialConfig (/Users/zhenyatelegin/Desktop/next.js/node_modules/@babel/core/lib/config/partial.js:66:16)\n @ multi ./pages/index.js' ],
  warnings: [] }
error An unexpected error occurred: "Command failed.
Exit code: 1
Command: sh
Arguments: -c next build
Directory: /Users/zhenyatelegin/Desktop/next.js/examples/with-absolute-imports
Output:
".
info If you think this is a bug, please open a bug report with the information provided in "/Users/zhenyatelegin/Desktop/next.js/examples/with-absolute-imports/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```

A follow-up to #4604: the dot in the regexp was not escaped as intended. By default `*` matches greedily, so the results are the same, but the new regexp should be more clear. Sorry for the mistake.

The prepares for next-server.

I also took this as an opportunity to get all build directory paths from a single location, as they were previously scattered across webpack/babel plugins and loaders.

Fixes #4572

This PR intends to address https://github.com/zeit/next.js/issues/4572 around documenting browser support and what needs polyfills.

There are many outstanding issues on the tracker regarding browser support and polyfills. This may alleviate some of them.

Fixes #4603.

Tests explain it the best:

```js
    describe('development mode (no chunkhash)', () => {
      it('should strip the extension from the filename', () => {
        const filename = 'foo_bar_0123456789abcdef.js'
        expect(getChunkNameFromFilename(filename, true)).toBe('foo_bar_0123456789abcdef')
      })

      it('should only strip the extension even if there\'s a hyphen in the name', () => {
        const filename = 'foo-bar-0123456789abcdef.js'
        expect(getChunkNameFromFilename(filename, true)).toBe('foo-bar-0123456789abcdef')
      })
    })

    describe('production mode (with chunkhash)', () => {
      it('should strip the hash from the filename', () => {
        const filename = 'foo_bar_0123456789abcdef-0123456789abcdef.js'
        expect(getChunkNameFromFilename(filename, false)).toBe('foo_bar_0123456789abcdef')
      })

      it('should only strip the part after the last hyphen in the filename', () => {
        const filename = 'foo-bar-0123456789abcdef-0123456789abcdef.js'
        expect(getChunkNameFromFilename(filename, false)).toBe('foo-bar-0123456789abcdef')
      })
    })
```

- Remove unused imports

- Edit some comments

- Rename Wrapper App Class

* remove `predeploy` scripts from `firebase.json` in favour of `npm` `pre` scripts as they are consistent across `deploy` and `serve` commands. (to revisit once Firebase add support in the `firebase.json` for `preserve`)
* update deps
* workaround some bug where Babel could not resolve the standard `next/babel` config. Explicitly defining this seems to remove the issue.
* closes #4562

Fixes #4581

Hello! I have got an error while building [gh-pages example](https://github.com/zeit/next.js/tree/canary/examples/gh-pages) with next 6.0.3. I have found solution to use CommonJS modules in `.babelrc`

This resolves #4227

This fixes a missed bug introduced in #4510.

Because the regexp was `/-[^-]*/` and not `/-[^-]*$/`, a wrong part of the filename was being removed:

```
bad:
'foo-bar-0123456789abcdef-0123456789abcdef.js' -> 'foo-0123456789abcdef-0123456789abcdef.js'

good:
'foo-bar-0123456789abcdef-0123456789abcdef.js' -> 'foo-bar-0123456789abcdef'
```

By a stroke of luck this didn't affect the existing dynamically generated chunks. To prevent regression I've added unit tests for the function that generates the name.

Btw. in the original issue (#4433) I used the right regexp, I just used the wrong regexp in #4510.

cc @timneutkens 

We don't need `.data` as `apollo.cache.extract()` returns at least `{}` when cache is empty

We don't pass apolloClient as props, so I removed the check as confusing and always false.

see https://github.com/zeit/next.js/blob/canary/examples/with-apollo-auth/lib/withApollo.js#L72-L75

Again please explain me if I am wrong :)

App component does not need/use apolloState prop, so let's remove it. If I'm wrong please explain me the purpose of this.

* Fix Access-Control-Request-Method header

* Make OPTIONS request work

React hot loader was removed already, the dependency still had to be removed.

Fixes one of the problems described in #4433.

The old regexp was removing everything after a hyphen, so with a chunk name like so:

```
chunks/path-to-a-file-[hash].js
```

the saved chunk name was

```
chunks/path
```

This caused problems, because webpack by default changes `/` to `-` in chunk names generated e.g. by ``import(`foo/${bar}`)``.

After this change the chunk name will be

```
chunks/path-to-a-file
```

* Added example for Ant Design with LESS

* Fix ESLINT

Since `_app.js` is used on every page it makes sense to move it's dependencies to the `commons.js` so that if you require a dependency in `_app.js` and in one of your pages it is not included twice in your bundles. 

This PR modifies the `CommonsChunkPlugin` to move every module that is used in `_app.js` and at least in one other bundle.

**Make amp example valid**

I'm using amp validator chrome plugin which shows that `meta charset=utf-8` is duplicated.
I assume that `Head` component adds `<meta charset="utf-8" class="next-head next-head">`
anyway.
And this line just duplicating it.

<img width="987" alt="screen shot 2018-06-06 at 15 54 45" src="https://user-images.githubusercontent.com/1488195/41036743-198ca00a-69a2-11e8-978c-5a5cb5a994d2.png">

Hello! I ran into an issue using typescript and jest with next 6.0.0. I was able to work through fixing it and I wanted to share my solution back to next.js, by upgrading the with-jest-typescript example to next 6.0.0.

The steps I followed were:

1. `npx babel-upgrade --write` which added babel-core@^7.0.0-bridge.0 to allow jest's babel 6 to play nice with next's babel 7
2. Remove `ts-jest` and replace with `babel-jest` to use babel to transform the typescript code, as is done when the dev and production builds run
3. Update the babelrc to use commonjs modules in test mode to be compatible with jest

Also, I removed the `NODE_ENV=test` on the jest task, because jest sets the env to test anyways, and I'm on windows where this code is incorrect. The other option is to use `cross-env` but I felt it was simpler to just remove the environment override.

To my knowledge, this PR would help on the following issues:

#3663 #4227 #4531 #4528 #4239 

* Make router properties update when re-rendering

* Remove documentation about methods that have been deprecated since v2/v3

* Update next export documentation

This was spread around the server. Now it's set in one place and passed around.

This was pulled from #4518, it can already be merged so it's easier to get it in.