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