Clean up UI, work on tutorial

src/items/Item.cpp

@@ -15,6 +15,7 @@ namespace ZL {
 			[&itemId](const Item& item) { return item.id == itemId; });
 		if (it != items.end()) {
 			std::cout << "Item removed from inventory: " << it->name << std::endl;
+			if (onItemRemoved) onItemRemoved(itemId);
 			items.erase(it);
 		}
 	}

src/items/Item.h

@@ -31,8 +31,9 @@ namespace ZL {
 		void clear() { items.clear(); }
 		size_t getCount() const { return items.size(); }
 
-		// Called whenever an item is added; receives the item id.
+		// Called whenever an item is added/removed; receives the item id.
 		std::function<void(const std::string&)> onItemAdded;
+		std::function<void(const std::string&)> onItemRemoved;
 	};
 
 } // namespace ZL