New beauty pages(404, 422, 500)

moving changelog note to unreleased section

New beauty pages(404, 422, 500)
Remove hard coded references to Active Record in railties
Merge pull request #9512 from Jacke/master

New 404, 422, 500 pages, they are more stylish and bring ruby essence…
ActiveSupport::Notifications::Instrumenter#instrument should yield
its payload the same way that ActiveSupport::Notifications does.
Fix spelling in test name.