Progress Update

Now supports drag and drop of items across the map from the inventory. The inventory logic is all in a single class: Inventory.cpp.
A transparent sprite is drawn when a user clicks on an item and drags it across the map.
The sprite is colored red (for now) and when the click is released, the item is "dropped" onto the map.

Future Work:

Support dragging and dropping items into crafting slots in the inventory menu.