This reduces the update cost of rooms changing, and fixes a bug where when a sublist became filtered it would change the notification count of the sublist.
This does change the expected usage of the state store to ensuring that only one place updates the rooms on the list states, which is currently the room list store. Ideally the state store could listen to the room list store to update itself, however due to a complicated require() loop it is not possible.
This cuts the render time in half (from ~448ms to ~200ms on my account) per received event, as we're no longer re-mounting the entire room list and instead just the section(s) we care about.
