Populate ActionItem model from bugzilla, polls and events.

* Sync [waiting <item>] action items from bugzilla.
* Sync pending_mentor_validation action items from bugzilla.
* Sync budget_needinfo action items from bugzilla.
* Sync council reviewer assignment action items from bugzilla.
* Change ActionItem model fields.
* Create action items only for bugs assigned to Reps.
* Add new action item on new poll.
* Resolve action item on new vote.
* Add new action item to submit post event metrics.
* Resolve action item when post event metrics are submitted.
I thought that this was better to be generic. If there is an open poll for the user's group we are creating an action item that is automatically closed after the poll's end (no need to go vote). We could although change the ``name`` and ``priority`` for automated budget votes to be more specific.