Show modal when event ends

- Create end event view
- Create end event template
- Show modal when event ends
Mark as done
Extend event
Reschedule event
Update announce text to reflect prompt
Issue #42: Prompt to finish event

As a user I want to be notified when an event ends to see if i've
finished it or have the option to reschedule it or extend it.

- Show modal when event ends
- Mark as done
- Extend event
- Reschedule event
- Update announce text to reflect prompt