Make Ved cache the overview map rendering

Make Ved cache the overview map rendering (maybe on level load, silently (without much CPU usage like it normally would when rendering the overview map), or the first time the map is opened), and when a room is updated (maybe like a few seconds after the room change), just change the part of the map that got updated. I’m sick and tired of this “Ved takes two fucking seconds every time I want to go to a different room that I don’t know the exact coordinates of”.