The `use_helpers` method was added in ViewComponent 3.8.0, and it's
included by default in all components since version 3.11.0.
Note we sometimes delegated the `can?` method to the controller instead
of the helpers, for no particularly reason. We're unifying that code as
well.
Adding, modifiying, and/or deleting questions for an already started
poll is far away from being democratic and can lead to unwanted side
effects like missing votes in the results or stats.
So, from now on, only modifiying questions will be possible only if
the poll has not started yet.
In this form, the only case where `poll` might be present without
`question.poll` being present to is going to be the `new` action. We can
assign the poll in the `new` action and get rid of the `poll` variable
in the form.
