This is required for automatically entering tab-complete mode because
onKeyDown is NOT called in that case, so we need to make sure to have a
membership list hanging around.
RoomView is the parent component which creates MessageComposer AND the status
bar. By making RoomView instantiate TabComplete we can scope instances
correctly rather than relying on singleton behaviour through dispatches. This
also makes communication between status bar and the MessageComposer infinitely
easier since they are now sharing the same TabComplete object.
Moved to a `TabComplete` class. Make it more generic (list of strings rather
than RoomMembers) and sort the member list by last_active_ago. Everything still
seems to work.
