For https://github.com/vector-im/riot-web/issues/13635
This is an incomplete implementation and is mostly dumped in this state for review purposes. The remainder of the features/bugs are expected to be in more bite-sized chunks.
This exposes the RoomListStore on the window for easy access to things like the new filter functions (used in debugging).
This also adds initial handling of "new rooms" to the client, though the support is poor.
Known bugs:
* [ ] Regenerates the entire room list when a new room is seen.
* [ ] Doesn't handle 2+ filters at the same time very well (see gif. will need a priority/ordering of some sort).
* [ ] Doesn't handle room order changes within a tag yet, despite the docs implying it does.
