Move mod vehicle registration to a decorator.

This cruft doesn't need to be in game.db, it can be kept with the mod
support code.

qt_ui/main.py

@@ -21,6 +21,7 @@ from game.profiling import logged_duration
 from game.server import EventStream, GameContext, Server
 from game.settings import Settings
 from game.theater.start_generator import GameGenerator, GeneratorSettings, ModSettings
+from pydcs_extensions import load_mods
 from qt_ui import (
     liberation_install,
     liberation_theme,
@@ -319,6 +320,8 @@ def main():
     if args.warn_missing_weapon_data:
         lint_all_weapon_data()
 
+    load_mods()
+
     if args.subcommand == "new-game":
         with logged_duration("New game creation"):
             game = create_game(