For any name not found in rooms data, rely on new
nio.HttpClient.get_displayname() function to get and cache it,
e.g. for our own name if no room is joined and past events from users
who left the room.
@futurize now returns PyQtFuture objects, wrapper for the
concurrent.futures.Future objects that can be used from QML,
to ensure name retrieval does not block the GUI.
- Trigger when room is shown if there's not enough messages to fill the
list height
- Trigger whenever user is scrolling before a certain point, instead of
when dragging is released/scrolling stopped and the top edge is hit
- Prevent multiple load requests at same time
- Keep a set of fully loaded rooms, don't request anymore history
if a room is fully loaded
