Model addition

Added some cool models (to my remote)
Added a method to give walls skins and edited the inner part of the castle
Fixed the unwanted collision problems, e.g. when a boss collides with a dead NPC they got stuck. I also fixed the bullets so that they don "kill" the cartridges. And I also made the critters drop cartridges randomly IF there is not a cartridge already in the game.
Added keeping track of the player statistics and displaying them at the end of the game.
Merge remote-tracking branch 'origin/master' into Joshie