Using arrays made it difficult to order by more than one field (like the
`most_voted` scope does), and so we were ordering by `confidence_score`
and ignoring the `created_at` column.
Using an AR relation makes it easy to reuse the existing `most_voted`
scope.
This change has one side effect: now comments with equal votes are
ordered in descending order instead of having no specific order. That
means flaky specs which failed sometimes because they assumed comments
were ordered by date are now always green.
I've also re-added the `oldest` scope removed in 792b15b thinking it was
removed because using it with arrays was too hard.
The `type: :feature` is automatically detected by RSpec because these
tests are inside the `spec/features` folder. Using `feature` re-adds a
`type: :feature` to these files, which will result in a conflict when we
upgrade to Rails 5.1's system tests.
Because of this change, we also need to change `background` to `before`
or else these tests will fail.
The now-deprecated `.trigger('click')` API simulated a click against
the DOM rather a click on the UI, which made our tests fragile and
wouldn't simulate actual user interaction
