Load HTML in ActionView not ActionPack

HTML Scanner is part of ActionView and it should be loaded along with it
Extend basic rendering, test it in railties
Describe BasicRendering shortly

[ci skip]
Move actionpack's controller tests
Move abstract's controller tests to AV

The ones that were actually testing AV functionality and should belong in there
Simplify if statements
Change description of BasicRendering#render

We're not dealing with templates here

[ci skip]
Fix formatting of error message

Make it oneliner
Merge pull request #12009 from wangjohn/fixtures_fix

Removing instances of string class_names in fixtures.
Merge pull request #12014 from wangjohn/change_deprecation_horizon

Changing deprecation_horizon to be Rails 4.2
Make AV dependency for ActionMailer
PG adapter deals with negative money values formatted with parenthesis.

Closes #11899.
Merge pull request #11396 from strzalek/extract_renderers

Remove dependency on Action View from Action Pack

This set of changes removes the need of using Action View with Action Pack.
Now you may use controllers without Action View, by rendering `:text` response
or alternatively you can plug in your own rendering logic. This is especially
handy when you're just dealing with APIs and don't need to include entire
Action View just to render simple JSON responses.
Merge pull request #11973 from prathamesh-sonpatki/nokogiri-warning

Add error message for including nokogiri in Gemfile for rake doc:guides
Merge pull request #11827 from vipulnsward/remove_extra_case

Remove extra case.
Merge pull request #11997 from startupjockey/add_credits_AS

Adds Akshay Surve to Rails Guides credits list [ci skip]
fix typo in the credit section of the guides. [ci skip]
Add Finder API changes to upgrading guide [skip ci]
Warning on doc for assets under lib|vendor not precompiling
Merge pull request #12015 from vipulnsward/add_dynamic_finders_to_upgrade

Add Finder API changes to upgrading guide [ci skip]