Don't tell the UI about CP TGOs.

These are an implementation quirk, and passing them to the UI just means
that we put TGO pins on top of the CP, which makes the base menu
unopenable.

In the old UI we avoided this by not drawing anything that was
`for_airbase`, but now that we can zoom in further we're drawing base
defenses.

game/theater/theatergroundobject.py

@@ -233,6 +233,11 @@ class TheaterGroundObject(MissionTarget):
     def is_factory(self) -> bool:
         return self.category == "factory"
 
+    @property
+    def is_control_point(self) -> bool:
+        """True if this TGO is the group for the control point itself (CVs and FOBs)."""
+        return False
+
 
 class BuildingGroundObject(TheaterGroundObject):
     def __init__(
@@ -354,7 +359,9 @@ class NavalGroundObject(TheaterGroundObject):
 
 
 class GenericCarrierGroundObject(NavalGroundObject):
-    pass
+    @property
+    def is_control_point(self) -> bool:
+        return True
 
 
 # TODO: Why is this both a CP and a TGO?