Implement StorageButton on HandsGUI and click empty hand to swap… (#517)

Also moved duplicate sprite view code to ItemSlotManager

Content.Client/UserInterface/IItemSlotManager.cs

@@ -9,5 +9,6 @@ namespace Content.Client.UserInterface
         void Initialize();
         bool OnButtonPressed(GUIBoundKeyEventArgs args, IEntity item);
         void UpdateCooldown(ItemSlotButton cooldownTexture, IEntity entity);
+        bool SetItemSlot(ItemSlotButton button, IEntity entity);
     }
 }