We were using the same logic in four different places, so we're creating
a new class to handle that logic.
Note that I didn't find a way to delegate the `content` method to a
`Admin::TableActionsComponent`, so we're delegating the `action` method
instead. That means we need to create a method returning an
`Admin::TableActionsComponent`. We also need to cache this object;
otherwise we were getting an error when calling `actions.action` from
the `Admin::Poll::Questions::TableActionsComponent`.
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.
