Add websocket event stream for sim updates.

As a proof of concept this only covers the flight positions.

game/sim/gameloop.py

@@ -72,6 +72,11 @@ class GameLoop:
         self.completed = True
 
     def send_update(self, rate_limit: bool) -> None:
+        # We don't skip empty events because we still want the tick in the Qt part of
+        # the UI, which will update things like the current simulation time. The time
+        # probably be an "event" of its own. For now the websocket endpoint will filter
+        # out empty events to avoid the map handling unnecessary events, but we still
+        # pass the events through to Qt.
         now = datetime.now()
         time_since_update = now - self.last_update_time
         if not rate_limit or time_since_update >= timedelta(seconds=1 / 60):