added isLeader Boolean with default to schema in groups_users table,ref #41
Added authorization, so that only admin can assign and unassign rooms to group, ref #16, ref #41
added membership model to fix group-user-relationship and add ability to access the group leader, ref #41
Added is_leader_of_group Function in user model, ref #41
Changed Group View to show membership and leadership of User, ref #41
Users can be degraded and promotet to Group Leaders, ref #41
Also adepted show- and edit-group views
Changed edit and show view of Group to make managing group Roles easier, ref #41
Added rights management, ref #41
Admins can do anything to a group,
Group Leaders can assign and unassign users and rename the group, they cannot promote or degrade and cannot unassign a group leader.
Added group leader role to tests and some more tests, ref #41
removed deprecated should, ref #41
maps image size

reduced image size
Merge branch 'Dolphins' of https://github.com/hpi-swt2/event-und-raumplanung into Dolphins
Never commit/push at midnight
Fixed broken tests, added missing tests, ref #41
Merged dev into B/feature/#41 (group leader mgmt), ref #41
Merge remote-tracking branch 'remotes/origin/dev' into Dolphins
migrate
calendar: changed color for approved&favored events
Merge branch 'dev' into B/feature/#41
Merge branch 'B/feature/#41' into Biber