* Create ItemSlotButton
* Refactor inventory buttons
Refactor so that KeyBind handling of inventory and hands are the same.
* Refactor InventoryInterfaceController to call ItemSlotManager with entities
This change allows HandsGUI and InventoryInterfaceController to just call ItemSlotManager.OnButtonPressed with an entity instead of a slot.
* Add CooldownCircle to ItemSlotButton
This allows Hands and Inventory to have cooldown circles on their ItemSlots.
* Refactor HandsGUI to use ItemSlots
This allows functionality and GUI to be the same between Inventory and Hands.
Added clicking empty hand to switch ActiveHand to clicked hand.
* Implement CooldownCircle in ItemSlotManager
Reorganize files
