Optionally group rooms by Discord categories #64

- Setting for this on the website - Setting can only apply when not using self-service mode - Hide the switch when in self-service? - Group the switch down lower with the self-service one? - Setting applies when syncing room or space - Would need to create a new space for each category - Cache these somewhere and reuse if the setting is toggled off and on? - Would need to update m.space.child in two rooms and two m.space.parent events in one room - Vanilla kstate diffing would struggle with this because if moving from one space to another it needs to know the ID of the old space in order to generate a removal event for the diff. But events are only generated based on the current state.