[SmashButton] Bulkier walls and using occlusion prevention

[Golfavel]

Currently, SmashButton has visibly thin walls, as to reduce the potential of obscuring anything from furniture, zombies, the player, etc., on the adjacent north/east tiles. This was done before the implementation of more sophisticated occlusion methods that the game now supports. Taking better advantage of the feature(s) should be looked into, in particular due to walls being so thin they can be perceived as having a floor where there is none.