Added relationship Group vs room, ref #16
Added funtionality to assign rooms to a group, ref #16
Added actions: manage_rooms, assign_room, unassign_room   to group_controller
Added Routes for all of them as group member routes
Added necessary views
TODO:Authentication still has to be done, as soon as admin role is defined
room can only be added to group, if not yet assigned ,ref #16
was still theoretically possible, by accessing the url
Added first tests for group_controller
Fixed Group Controller Assignment POC Test, ref #16
by reloading local variables from the database
Merged dev into feature/Grouprooms
Fixed Group Room Assignment test after merge, ref #16