fixing the null pointer exception crash.

modified:   src/game/GameLoop.java
major cleaning before update the inventory behaviour to
fit the modification made in the game desgin document, namely
adding specific equipment slots, and carrying battery.

modified:   src/entity/LivingEntity.java
modified:   src/event/control/PlayerControl.java
deleted:    src/userInterface/Inventory.java
new file:   src/userInterface/inventory/Inventory.java
new file:   src/userInterface/inventory/InventoryItemEnum.java
the inventory now handles 5 specific slots, allowing for the handling
of the equipment active skills

modified:   src/entity/player/Player.java
modified:   src/userInterface/inventory/Inventory.java
modified:   src/userInterface/inventory/InventoryItemEnum.java
adding the new item Battery by modifying MetalJunk
new file:   assets/textures/battery.png
deleted:    assets/textures/metalJunk.png
modified:   src/game/GameLoop.java
renamed:    src/item/MetalJunk.java -> src/item/Battery.java
modified:   src/rendering/TextureManager.java
fixing bugs due to a quick commit

modified:   src/game/GameLoop.java
modified:   src/rendering/TextureManager.java
Merge branch 'master' into inventory
adding an item manager

modified:   src/entity/npc/LivingEntityManager.java
modified:   src/environment/Map.java
modified:   src/environment/room/Room.java
modified:   src/environment/room/SpawnRoom.java
modified:   src/game/GameLoop.java
new file:   src/item/ItemManager.java
Merge branch 'master' into inventory
handling of the battery by the inventory
pressing f when carrying one drops it

modified:   src/entity/player/Player.java
modified:   src/environment/Map.java
modified:   src/environment/room/Room.java
modified:   src/event/control/PlayerControl.java
modified:   src/userInterface/inventory/Inventory.java
modified:   src/userInterface/inventory/InventoryItemEnum.java
Merge branch 'master' into gui