adding a new level of inheritance to represent the
possibility to equip an object

new file:   src/item/Equipment.java
modified:   src/item/Item.java
modified:   src/item/weapon/Weapon.java
first step to factorize a table handling in inventory
the class is implemetnd as genericly as possible and may
therefore be reused

new file:   src/utils/NonContinuousTable.java