remove duplicate event creation for command /event create

[LociStar]

Issue: If a user is creating an event with the same name, he is only able to edit/ schedule the first one. Also deleting events, that exists with the same name could lead to issues, where the event id is not deleted from DBUser.

Possible Solutions:

• Make a selection for the user, if he has multiple events with the same name
• Only allow event titles with different names for a user
• Rename the event, if it has a exsisting name (e.g. add (1))
• Rename the event, but do not display the counter for duplicated events in the event title

[LociStar]

Done. I used the most simple solution: One user can not use the same name for multiple events.