The locale config is set in application.rb from environment variables
already. We don't need to repeat that logic in test.rb. And because it
was outdated, the language switcher was actually broken in the test
environment. We did have an English selector for the fallback `en` even
though we were already displaying English as en_TST. And after
switchting to Spanish, we could switch back because en_TST was not in
the available locales.
I now fixed the test with the right assumption and the config to solve
the problem.
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`.
