Rethink External Eventsignups

Created by: hermannsblum

It was requested by the Kulturteam that every attendant of an event should have a name in the list if participants. So far, we are only storing email adresses from externals. Of course we could add an option that additional_fields will contain a form for the name in case of external signup, and then reapply a mapping to this data when requesting the list of participants.

However, this makes me think that it would make the API interface and later maintainance, aswell as any UI much easier if we would just request external participants to create their own account. The functionality is mostly there already for extraordinary members, aswell as the current email validation for the eventsignups, which would be moved into the users instead. What do you think?

_{Sent with GitHawk}