editing constraints for events

[MarcelSchmidberger]

As participant / Organizer
I dont want an event to change completely after it started
In order to prevent confusion due to changes

Acceptance Criteria

• Teilnehmerzahl, Anmeldefrist, Startdatum, Teilnahmeform und Spielsystem (and Anfangswert for ranking lists) should not be changeable after event start
• Name, Beschreibung, Enddatum, Spieltaglänge can be changed later on
• admin may change everything

[MarcelSchmidberger]

no change of team and singel player
max zahl constraints

[MarcelSchmidberger]

when changing the join limit date of an event where matches have already been entered I get this error:

[MarcelSchmidberger]

As I see this issue needs to be updated, please ask me before you start working on it and use your common sense for judging which field should be changeable when.