Delete event

Created delete-event.

Only not-active events can be deleted
Deletion is done via setting deleted to true (didn't follow the "active" pattern because in the context of event, the word active has already a meaning).

Basically what it does is not showing the event in the past-events parts - therefor it looks like for the user as it is deleted.

"Real" deletion from the database was not implemented (we do not delete on other places and have references to this event ...
real world scenario: why delete data? keep it for statistics or so ...)