We removed the link to this page in commit 83e8d6035 because poll
questions don't really make sense without a poll.
However, this page also contained information about successful
proposals, which might be interesting so administrators don't have to
navigate to the public area in order to find and create questions based
on successful proposals.
So we're keeping the part about successful proposals and linking it from
the proposals part of the admin area.
Note we're using translation keys like `successful_proposals_tab`, which
don't make sense anymore, for the successful proposals. We're doing so
because we've already got translations for these keys and, if we renamed
them, we'd lose the existing translations and our translators would have
to add them again.
Also note we're changing one poll question test a little bit so we
create the question from a successful proposal using the new page. There
are other tests checking how to create a question from the
admin/proposals#show action and other tests checking what happens when
accessing a successful proposal in the admin section, so we don't lose
any test coverage by changing an existing test instead of adding a new
one.
Finally, note that we've removing the `search` method in poll question
because we no longer use it. This currently makes the
`author_visible_name` database column useless; we aren't removing it
right now because we don't want to risk a possible data loss in a patch
release (we're about to release version 2.3.1), but we might remove it
in the future.
This is consistent to what we usually do. Also, we're applying the same
criteria mentioned in commit 72704d776:
> We're also making these actions idempotent, so sending many requests
> to the same action will get the same result, which wasn't the case
> with the `toggle` action. Although it's a low probability case, the
> `toggle` action could result in [selecting a proposal] when trying to
> [deselect] it if someone else has [deselected it] it between the time
> the page loaded and the time the admin clicked on the "[Selected]"
> button.
The button to select/deselect a proposal wasn't very intuitive; for
example, it wasn't obvious that pressing a button saying "selected"
would deselect the proposal.
So we're using a switch control, like we do to enable/disable features
since commit fabe97e50.
