Convert save file format to use new minification

[ChrisNeedham24]

• In #150, for multiplayer, minification of game models was required in order to send them as packets to and from the game server.
• In the process of doing this, a way to minify quads was found that is far better than the existing save file format.
• Currently quads take up something north of 80% of actual save file content, so it would be good to reduce this.
• However, we would have to make sure that the old format is still supported, though that should be easy to do in save_migrator.py.
• It might be worth considering replacing the whole save file format with its minified equivalent as well, though that isn't strictly required for this issue to be resolved.

[ChrisNeedham24]

Acceptance Criteria:

• When saving games in save_game() in game_save_manager.py, each quad should be minified using the minify_quad() function from minifier.py before persisting the save's data.
• Loading games must still work using the new format.
• Update migrate_quad() in save_migrator.py to initially use inflate_quad() from minifier.py, and then fallback to the original implementation.
• Consider whether it would be worth storing the game's players and heathens in their minified forms as well, and implement if so, following the same process as the above points.