Re-add tests for room list sorting behaviour

[turt2live]

Now that there's a new room list algorithm, we need tests to make sure it sorts things correctly. This is higher priority because bugs keep cropping up with the implementation.

[turt2live]

I'm going to go ahead and bump this out of the current sprint (which ends pretty quick here) because nothing in the chain here has testability in mind. Tests are a good thing that we should have, but the SettingsStore wasn't really made with testing in mind, nor was Unread. There's a lot more work to do this than what appears on the surface.

Edit: I've pushed what I do have though, for anyone who wants to pick this up later: matrix-org/matrix-react-sdk@b7db917

[Johennes]

Closing because RoomListStore appears to have tests now.