Remove/delete rooms & spaces

Like matrix-org/matrix-spec-proposals#722, which has been falsely closed as a duplicate of matrix-org/matrix-spec#242, I still think it should be possible to delete rooms without any shell script or other magic. We're using Matrix for some weeks now and are VERY happy with it, but the inability to really *delete* rooms (and NOT just hide them) is a major annoyance. I dont want to give all my coworkers SSH access to the chat server and tell them to run a shell-script just so they can delete rooms they've created. I'm aware of the fact that when federation is enabled you cannot really guarantee that the room is actually deleted. But: We have already the option during room creation to define a room as server-local. At the very least these rooms should be deletable IMHO.

Start by reading matrix-org/matrix-spec-proposals#722 and matrix-org/matrix-spec#242, then review the issue discussion for the existing deletion expectations. Done means users can delete rooms they created without SSH access or shell scripts, with the behavior for federated rooms and server-local rooms explicitly defined.

Written by the indexing model from the issue text.