Better noise/smoke handling

savegame_legacy: Seems to be outdated since none of the caches are updated. I added refresh() there in the hopes that would make it more correct, but this needs testing.
Removed cached exhaust and made it possible to call the function more often, which is needed for future vehicle overhaul. Atm it's still called twice per turn, will be fixed in the turn handling bit coming up.
Driving in reverse spawns exhaust in front of the vehicle, no more choking on own exhaust.
Cached exhaust stuff removed, not needed.
Added more sound messages.
noise: Cars now make noise proportionally to how much they're using their engines.
smoke: Rebalanced, exact numbers could probably be tuned.
mufflers: Less effective when they become damaged.