Add arrival/divert airfield selection.

Breaks save compat because it adds new fields to `Flight` that have no
constant default. Removing all of our other save compat at the same
time.

Note that player flights with a divert point will have a nav point for
their actual landing point. This is because we place the divert point
last, and DCS won't let us have a land point anywhere but the final
waypoint. It would allow a LandingReFuAr point, but they're only
generated for player flights anyway so it doesn't really matter.

Fixes https://github.com/Khopa/dcs_liberation/issues/342

gen/flights/flight.py

@@ -65,6 +65,7 @@ class FlightWaypointType(Enum):
     INGRESS_DEAD = 20
     INGRESS_SWEEP = 21
     INGRESS_BAI = 22
+    DIVERT = 23
 
 
 class FlightWaypoint:
@@ -133,12 +134,15 @@ class FlightWaypoint:
 class Flight:
 
     def __init__(self, package: Package, unit_type: FlyingType, count: int,
-                 from_cp: ControlPoint, flight_type: FlightType,
-                 start_type: str) -> None:
+                 flight_type: FlightType, start_type: str,
+                 departure: ControlPoint, arrival: ControlPoint,
+                 divert: Optional[ControlPoint]) -> None:
         self.package = package
         self.unit_type = unit_type
         self.count = count
-        self.from_cp = from_cp
+        self.departure = departure
+        self.arrival = arrival
+        self.divert = divert
         self.flight_type = flight_type
         # TODO: Replace with FlightPlan.
         self.targets: List[MissionTarget] = []
@@ -157,6 +161,10 @@ class Flight:
             custom_waypoints=[]
         )
 
+    @property
+    def from_cp(self) -> ControlPoint:
+        return self.departure
+
     @property
     def points(self) -> List[FlightWaypoint]:
         return self.flight_plan.waypoints[1:]