Feature unload after exit

This feature allow a level to be unloaded when it is exited, even if the total level play is not finished yet. If a level uses the same dungeon sublevel twice, and that dungeon has coins, currently when the dungeon is entered the second time, it is in the same state it was the first time when it was exited.

What this does is add a level setting, so when the dungeon is exited the first time, it can unload. Then when it is entered the second time, it will reload and all the coins, enemies, or whatever will be back.