Moderators for rooms

Room creators should be able to add an account as a moderator for a room. Moderators should have the same rights as the creator with the one exception of not being allowed to delete the room.

added enhancement label

API is ready, will implement frontend logic in the forseeable future

assigned to @tksl38

mentioned in issue #233 (closed)

changed milestone to %v1.3

added ToDo label

removed ToDo label

assigned to @lmas60 and unassigned @tksl38

mentioned in merge request !195 (merged)

closed via merge request !195 (merged)

mentioned in commit f6ffae27

mentioned in commit 5efbb0fb