Admin users should be able to push "Event full" notifications out from the app to users attending the event, suggesting other events to go to instead.

[harryslimes]

1. Create event_full variable in database for events
2. When listing events in UI render "Full" badge if event_full = true. UI LOCATIONS currently: Programme, Personal Calendar
3. Allow events to be marked as full in admin panel
4. Create "Event Full" push notification that links to events page (edited)
5. Nice to have: Link 3+4 with canned message for notification including name of event