There were a few changes needed:
* Plugins are now specified through `plugin:` config keyword.
* All plugin gems need to be specified explicitly in Gemfile since they
are no longer dependencies of plugins already specified explicitly.
* All plugin gems need to be updated in other to use the new APIs.
* One cop was renamed.
* New offenses safe to correct were corrected directly with `bundle exec
rubocop -a`.
* New offenses unsafe to correct were added to the TODO configuration
with `bundle exec rubocop --auto-gen-config --auto-gen-only-exclude
--exclude-limit 1400 --no-auto-gen-timestamp`.
The route and controller were in the main app and the views in the engine, with this commit they stay all inside the engine
This is done to keep it simple and remove the unnecessary dependency between main app and engine
If we use this mechanism in the future for other things in the main app or other engines, we can find a way to extract/abstract this
