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.
You can move this inside the `ActionItem` model. All you need is to update the `completed` field to `True` to each ActionItem instance.