Fixes #4494

This resolves the

> .value is not a valid Plugin property

error showing up for people in https://github.com/zeit/next.js/issues/4227

cc @timneutkens 

* This is minor refactoring.
* Apply alphabetical order to files list.

This reverts commit b970e25e.

Fixes #4268

Fixes zeit/styled-jsx#425
Fixes #4246
Fixes #4273

* Upgrade react hot loader

* Upgrade to 4.1.1

* Use update-check

* Check for tty

* Handle production errors correctly

* Improved source map support

* Make react-hot-loader hold state again

* Remove console.log

* Load modules on demand

* Catch errors in rewriteErrorTrace

* Update comment

* Update comment

* Remove source-map-support

* Load modules in next-dev

* Make sure error logged has sourcemaps too

* Add tests for production runtime errors

* Add tests for development runtime errors. Fix issue with client side errors in development

* Move functionality back to renderError now that error handling is consistent

* Rename to applySourcemaps

# Conflicts:
#	yarn.lock

* Expose pages/_app.js

* Add tests for _app and _document

* Uncomment deprecation warnings

* Add documentation for _app, improve documentation of _document

* Update docs / test for _document

* Add _document to client compiler in development

* Add missing app.js to comment

* Only warn once

* Add url-deprecated error page

* Combine tests

* Yse same message for all methods of ‘props.url’

* Update docs around _app

* Update documentation

* Quotes

* Update table of contents

* Add build manifest

* Split out css since they don’t have exact name

* Remove pages map

* Fix locations test

* Re-run tests

* Get consistent open ports

* Fix static tests

* Add comment about Cache-Control header

Upgrade Babel 6 to Babel 7 (major)

* Better support React 16.3.0

https://github.com/mridgway/hoist-non-react-statics/pull/43

* Lock version