Schedule Editor: Don't allow creation of events with same start and end date

[SVNKoch]

When trying to save, it will result in
Invalid time range, from 07:15:00 is after 07:15:00 for dictionary value @ data['friday']. Got [{'from': '07:15', 'to': '07:15'}]
thus creating should not be possible from the start (disabled save button)

PS: pressing enter in the above edit screen (see image), will not save the data but instead discard it