Added support for closing doors
Renamed and added some textures for the doors
Added so the spritename is saved in the instance
Doors now change textures based on if its open or closed
Renamed textures
Cleaned up the class, and javadoced
Fixed bug with doors not closing
Fixed so stairs spawns player at right position
Merge branch 'doors' into dev

Conflicts:
	se/chalmers/roguelike/World/LevelGenerator.java
Merge branch 'stairs' into dev

Conflicts:
	se/chalmers/roguelike/Engine.java
	se/chalmers/roguelike/Entity.java
	se/chalmers/roguelike/World/LevelGenerator.java