Add shipping lane support to campaign files.

These don't actually do anything yet, this is just the campaign support
and UI.

https://github.com/Khopa/dcs_liberation/issues/826

game/theater/controlpoint.py

@@ -267,6 +267,7 @@ class ControlPoint(MissionTarget, ABC):
         # TODO: Should be Airbase specific.
         self.has_frontline = has_frontline
         self.connected_points: List[ControlPoint] = []
+        self.shipping_lanes: Dict[ControlPoint, List[Point]] = {}
         self.convoy_spawns: Dict[ControlPoint, Point] = {}
         self.base: Base = Base()
         self.cptype = cptype
@@ -397,6 +398,9 @@ class ControlPoint(MissionTarget, ABC):
         self.convoy_spawns[to] = convoy_location
         self.stances[to.id] = CombatStance.DEFENSIVE
 
+    def create_shipping_lane(self, to: ControlPoint, waypoints: List[Point]) -> None:
+        self.shipping_lanes[to] = waypoints
+
     @abstractmethod
     def runway_is_operational(self) -> bool:
         """