further inventory implementation
	LivingEntity now has an inventory
	the Inventory is displayed when pressing "i"
	more work needs to be done for the appearance of the inventory

modified:   src/entity/LivingEntity.java
modified:   src/entity/npc/LivingEntityManager.java
modified:   src/entity/npc/Npc.java
modified:   src/entity/npc/Zombie.java
modified:   src/entity/player/Player.java
modified:   src/event/control/PlayerControl.java
modified:   src/game/GameLoop.java
modified:   src/inventory/Inventory.java
modified:   src/userInterface/OverlayManager.java
modified:   src/userInterface/PlayerStatsOverlay.java