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 `login_as_admin_and_visit` helper was used a lot but isn't really
shorter than:
login_as_admin
visit path_visit
Calling those methods separately reduces line length. It also removes
the potential impression that it may be more efficient to use the
helper. Now we have less indirection if one of the calls fails and see
the failing spec line straight away.
