AEW&C kneeboard + actually do AEW&C (#922)

* AEW&C will now do AEW&C
* AEW&C gets a frequency
* AEW&C is added to kneeboard (Frequency, Depature, Depature Time, Arrival Time)

gen/flights/flightplan.py

@@ -713,6 +713,10 @@ class AwacsFlightPlan(LoiterFlightPlan):
         if self.divert is not None:
             yield self.divert
 
+    @property
+    def mission_start_time(self) -> Optional[timedelta]:
+        return self.takeoff_time()
+
     def tot_for_waypoint(self, waypoint: FlightWaypoint) -> Optional[timedelta]:
         if waypoint == self.hold:
             return self.package.time_over_target