Airlift support.

UI isn't finished. Bulk transfers where the player doesn't care what
aircraft get used work (though they're chosen with no thought at all),
but being able to plan your own airlift flight isn't here yet.

Cargo planes are not implemented yet.

No way to view the cargo of a flight (will come with the cargo flight
planning UI).

The airlift flight/package creation should probably be moved out of the
UI and into the game code.

AI doesn't use these yet.

https://github.com/Khopa/dcs_liberation/issues/825

gen/ato.py

@@ -8,6 +8,8 @@ example, the package to strike an enemy airfield may contain an escort flight,
 a SEAD flight, and the strike aircraft themselves. CAP packages may contain only
 the single CAP flight.
 """
+from __future__ import annotations
+
 import logging
 from collections import defaultdict
 from dataclasses import dataclass, field
@@ -172,6 +174,7 @@ class Package:
             FlightType.OCA_RUNWAY,
             FlightType.BAI,
             FlightType.DEAD,
+            FlightType.TRANSPORT,
             FlightType.SEAD,
             FlightType.TARCAP,
             FlightType.BARCAP,