Event scheduling can be changed to end in the past
Steps to reproduce
While creating a scheduled event which ends in the past is prevented by the admin-UI, editing an event to be in the past is not.
Steps to reproduce:
1. Schedule an event
2. Open Event Details -> Scheduling and change the start and end dates/times to be in the past
Actual Results: No error shown, data is saved
Expected Results: Error is shown, data is not saved