Multiple autosaves?#582

Instead of one, keep the last N autosave files.

This came as a request to the Twilight Imperium mod from a player wanting to rewind game state, but I could see it save the day for the occassional wrecked game where a griefer joins and messes with the table state (the games use “well known” passwords and usually welcome spectators) and autosave overwrites with a bad version.

I’m aware there’s a permission that would prevent griefers from taking an empty seat and messing with the board, players rarely set it.