Logout problems #36
Description
When the WebSocket is closed, the collaborator is not "leaved" from its collaborative sessions. This is intended, so that the collaborator may go online again. However, if the collaborator never goes online again, synchronization is impossible when resolving conflicts.
So, we should implement a timout / an "inactive" collaborator concept to avoid that. Or just leave all collaborative sessions on WebSocket close, but let the collaborator instance live (then offline editing is impossible, but at least we can sign in again as the same collaborator).