Add off-map spawn locations.

The AI isn't making use of these yet, but it's not smart enough to do so
anyway.

Would benefit from an icon to differentiate it on the map.

I'm stretching the definition of "control point" quite a bit. We might
want to put a class above `ControlPoint` for `AirSpawnLocation` to
represent types of spawn locations that can't be captured and don't have
ground objectives.

Fixes https://github.com/Khopa/dcs_liberation/issues/274

qt_ui/widgets/map/QMapControlPoint.py

@@ -79,11 +79,8 @@ class QMapControlPoint(QMapObject):
 
         for connected in self.control_point.connected_points:
             if connected.captured:
+                menu.addAction(self.capture_action)
                 break
-        else:
-            return
-
-        menu.addAction(self.capture_action)
 
     def cheat_capture(self) -> None:
         self.control_point.capture(self.game_model.game, for_player=True)