Manage usable Items and their function + create ItemChoiceWindow

[Unarelith]

• Manage usable Items and their function
  • A virtual base class ItemAction
  • Child classes ItemHealAction or ItemDamagesAction, or ItemMapAction => Give a way to check conditions before being able to use an item
• Create a new class ItemChoiceWindow which represents all the possibilities to do with the Item we choosed ( For example a potion have a choice "Use" which change the mode to ChooseActorTarget )