Add bare actionview gem to the root directory

This commit creates structure for Action View gem and is first of a
series of commits extracting Action View from Action Pack.
Move actionpack/lib/action_view* into actionview/lib
ActionView version should be 4.1.0
Move template tests from actionpack to actionview
Remove unneeded files
Add actionpack as actionview's development dependency

ActionView still relies on ActionPack in some of the tests.
Remove unneeded test fixtures in AV
Copy company test fixture to AV (fixes failing test)
Remove digestor fixtures from AP

They were moved to actionview/ and are not used in actionpack
Fix digestor tests
Remove require to AP stuff that left
Template test were moved to AV
Add ActionView to CI
Fix isolated tests on AV
Change from 'actionpack' to 'actionview' for locales path
Remove heading from AV's CHANGELOG
Adjust changelog for AV & AP
Bump up version, fix module name
Rename AP to AV in info about running tests
Restore mistakenly removed malformed file fixtures