Move the AI to the normal procurement system.

The procurement AI now uses the same system as the players. Orders are
placed and take a turn to fulfill.

This has a few advantages:

* We no longer need special case purchase logic for the turn 0
  population of opfor airbases.
* Players using auto-purchase can cancel orders they don't like.

game/game.py

@@ -91,9 +91,7 @@ class Game:
         self.__destroyed_units: List[str] = []
         self.savepath = ""
         self.budget = PLAYER_BUDGET_INITIAL
-        # The enemy currently doesn't buy anything on turn zero; they get
-        # pre-populated airbases that are generated by the new game generator.
-        self.enemy_budget = 0
+        self.enemy_budget = PLAYER_BUDGET_INITIAL
         self.current_unit_id = 0
         self.current_group_id = 0
 
@@ -110,6 +108,8 @@ class Game:
             cp.pending_unit_deliveries = self.units_delivery_event(cp)
 
         self.sanitize_sides()
+        # Turn 0 procurement.
+        self.plan_procurement()
         self.on_load()
 
     def generate_conditions(self) -> Conditions:
@@ -229,24 +229,8 @@ class Game:
             control_point.process_turn()
 
         self.process_enemy_income()
-        self.enemy_budget = ProcurementAi(
-            self,
-            for_player=False,
-            faction=self.enemy_faction,
-            manage_runways=True,
-            manage_front_line=True,
-            manage_aircraft=True
-        ).spend_budget(self.enemy_budget)
 
         self.process_player_income()
-        self.budget = ProcurementAi(
-            self,
-            for_player=True,
-            faction=self.player_faction,
-            manage_runways=self.settings.automate_runway_repair,
-            manage_front_line=self.settings.automate_front_line_reinforcements,
-            manage_aircraft=self.settings.automate_aircraft_reinforcements
-        ).spend_budget(self.budget)
 
         if not no_action and self.turn > 1:
             for cp in self.theater.player_points():
@@ -288,6 +272,27 @@ class Game:
                 gplanner.plan_groundwar()
                 self.ground_planners[cp.id] = gplanner
 
+        self.plan_procurement()
+
+    def plan_procurement(self) -> None:
+        self.budget = ProcurementAi(
+            self,
+            for_player=True,
+            faction=self.player_faction,
+            manage_runways=self.settings.automate_runway_repair,
+            manage_front_line=self.settings.automate_front_line_reinforcements,
+            manage_aircraft=self.settings.automate_aircraft_reinforcements
+        ).spend_budget(self.budget)
+
+        self.enemy_budget = ProcurementAi(
+            self,
+            for_player=False,
+            faction=self.enemy_faction,
+            manage_runways=True,
+            manage_front_line=True,
+            manage_aircraft=True
+        ).spend_budget(self.enemy_budget)
+
     def message(self, text: str) -> None:
         self.informations.append(Information(text, turn=self.turn))