Revert "Move setting content_type to AV"

This reverts commit f4d602aff6cec80304b131ecfcc2676d0304f0cc.
Add missing require
Remove dependency on AV
Require log_subscriber
Do not load AV inside AP

Move that part to AV railtie
Remove hard require to ActionView from ActionMailer
Add AV as development dependency for railties

It's needed for tests
Add missing requires inside AV
Include AV railtie in railties isolation tests
Missing AV requires in railties tests
Include AV railtie when we're not loading full rails stack
Add --skip-action-view to app generator
Add #rendered_format method to controllers
Do not include action_view/layouts

We don't need them. They'll be loaded automaticly if AV will be included
Fist stab on basic rendering
Move render_test to AV
Split rendering tests between AP & AV

All rendering test remain in AV. Head, ETag etc. test stay in AP
Remove unused fixtures and models from AP tests
Cleanup & reorganise rake tasks in AV
Add AP tests to runner