Inventory Input (#503)

* 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

Content.Client/Interfaces/GameObjects/Components/Items/IHandsComponent.cs

@@ -12,5 +12,6 @@ namespace Content.Client.Interfaces.GameObjects
 
         void SendChangeHand(string index);
         void AttackByInHand(string index);
+        void UseActiveHand();
     }
 }