The all entities can now open doors. (but not close them)

This was trickier than expected, to let the monsters that can open doors pathfind
through doors I had to let each monster have it's own dungeon_map.
Since they are no longer shared the dungeon_level can no longer cache the dungeon_map.
This caused a performance hit, I may have to look into performance again soon.

Also the walkable_positons cache had to be removed, many monsters walking
randomly will be slow.