Allow some users to register other users as participants for events
|Priority:||Should have||Due date:|
|Assignee:||Thomas Ernst||% Done:||
|Target version:||Version 0.7.0|
Some users (namely the ones responsible for an event) should be able to add other users as participants to the event. This could be helpful e.g. if somebody tells that he will participate but does not register itself at the website.