This reverts commit 82a7593e.

Capybara was updated in teamcapybara/capybara#1841 to use Minitest style
assertions so that system test output shows x number of assertions, x
numbe of failures, etc.

Before:

```
6 runs, 0 assertions, 0 failures, 0 errors, 0 skips
```

After:

```
6 runs, 7 assertions, 1 failures, 0 errors, 0 skips
```

This change bumps Capybara from 2.7.0 to 2.13.0 and includes the
required minitest assertion file in the test case. 🎉

* Move system tests back into Action Pack
* Rename `ActionSystemTest` to `ActionDispatch::SystemTestCase`
* Remove private base module and only make file for public
`SystemTestCase` class, name private module `SystemTesting`
* Rename `ActionSystemTestCase` to `ApplicationSystemTestCase`
* Update corresponding documentation and guides
* Delete old `ActionSystemTest` files

Renames `Rails::SystemTestCase` to `ActionSystemTest` and moves it to a
gem under the Rails name.

We need to name the class `ActionSystemTestCase` because the gem expects
a module but tests themselves expect a class.

Adds MIT-LICENSE, CHANGELOG, and README for the future.

* Adds test case test
* Adds driver adapter test
* Adds tests for capybara seleium driver (testing the settings not
actually opening the browser to test capybara w/ selenium because that
would so so so slow)
* Adds tests for rack test driver
* Adds tests for generators

which is bundled in new apps by default

* puma 3.7.0: to let kill("TERM") properly terminate the process in railties test (3.6.2 doesnot on my machine)
* amq-protocol 2.1.0: to reduce warnings in AJ tests
* rails-html-sanitizer: missing change in a previous commit that updated Gemfile

Erubi offers the following advantages for Rails:

* Works with ruby's --enable-frozen-string-literal option
* Has 88% smaller memory footprint
* Does no freedom patching (Erubis adds a method to Kernel)
* Has simpler internals (1 file, <150 lines of code)
* Has an open development model (Erubis doesn't have a
  public source control repository or bug tracker)
* Is not dead (Erubis hasn't been updated since 2011)

Erubi is a simplified fork of Erubis that contains just the
parts that are generally needed (which includes the parts
that Rails uses).  The only intentional difference in
behavior is that it does not include support for <%=== tags
for debug output.  That could be added to the ActionView ERB
handler if it is desired.

The Erubis template handler remains in a deprecated state
so that code that accesses it directly does not break.  It
can be removed after Rails 5.1.

This reverts commit 8c155c93.

Not really 😢

This reverts commit 66e5b9d3.

We're seeing some test failures in AR postgresql tests

I see no reason not to use the newest stable version.

this fixes sqlite3-1.3.12/lib/sqlite3/pragmas.rb:301: warning: method redefined; discarding old integrity_check

nio4r 2.0.0 primarily includes new features and bugfixes, with few breaking
changes. The primary reason for bumping the major version is dropping support
for all Ruby versions prior to 2.2.2, so as to match Rails 5.

Full release announcement here:

https://groups.google.com/forum/#!topic/socketry/ZDIUj1ufiJ8

These lines were lost in https://github.com/rails/rails/commit/774be3ea3b9d25ab69daf11c5071deaf053d7d5b#diff-e79a60dc6b85309ae70a6ea8261eaf95L204.

Bumped to Ruby 2.4 compatible versions

Coffee script 1.12.1 was released and contained a bug where coffee
script was undefined. 1.12.1 was yanked and 1.12.2 was released. This
bumps coffee-script-source so that CI Railties tests pass.

See: https://github.com/jashkenas/coffeescript/issues/4403

https://travis-ci.org/rails/rails/jobs/165766716#L506