adding the MetalJunk item

new file:   assets/textures/metalJunk.png
new file:   src/item/MetalJunk.java
modified:   src/rendering/TextureManager.java
factorizing the graphic texture code into GraphicsAL

modified:   src/entity/LivingEntity.java
modified:   src/entity/npc/Zombie.java
modified:   src/entity/player/Player.java
modified:   src/game/GameLoop.java
modified:   src/item/weapon/LaserRifle.java
modified:   src/rendering/Background.java
modified:   src/utils/GraphicsAL.java
Merge branch 'master' into items
adding a new item plus some refactoring

modified:   src/game/GameLoop.java
renamed:    src/item/weapon/LaserRifle.java -> src/item/Item.java
modified:   src/item/MetalJunk.java
modified:   src/item/weapon/LaserRifle.java
Merge branch 'master' into inventory