Add migrator

Attempts to fix incompatibilities in save files across builds. The idea is to try and handle the incompatibility as graceful as possible, and adding more "incompatibility fixes" in the future.

game/__init__.py

@@ -1,2 +1,3 @@
 from .game import Game
 from .version import VERSION
+from .migrator import Migrator

game/migrator.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from game.ato.packagewaypoints import PackageWaypoints
+from game.data.doctrine import MODERN_DOCTRINE, COLDWAR_DOCTRINE, WWII_DOCTRINE
+from game.utils import knots, feet, nautical_miles
+
+if TYPE_CHECKING:
+    from game import Game
+
+
+class Migrator:
+    def __init__(self, game: Game):
+        self.game = game
+        self._migrate_game()
+
+    def _migrate_game(self) -> None:
+        self._update_doctrine()
+        self._update_packagewaypoints()
+
+    def _update_doctrine(self) -> None:
+        doctrines = [
+            MODERN_DOCTRINE,
+            COLDWAR_DOCTRINE,
+            WWII_DOCTRINE,
+        ]
+        for c in self.game.coalitions:
+            if c.faction.doctrine.__dict__ in [d.__dict__ for d in doctrines]:
+                continue
+            found = False
+            for d in doctrines:
+                if c.faction.doctrine.rendezvous_altitude == d.rendezvous_altitude:
+                    c.faction.doctrine = d
+                    found = True
+                    break
+            if not found:
+                c.faction.doctrine = MODERN_DOCTRINE
+
+    def _update_packagewaypoints(self) -> None:
+        for c in self.game.coalitions:
+            for p in c.ato.packages:
+                if not hasattr(p.waypoints, "initial"):
+                    p.waypoints = PackageWaypoints.create(p, c)