Created InventoryItemModel class in rpki.inv.__init__.py
Renamed methods in Inventory class (ex: Inventory.addItem -> Inventory.add)
Removed __setitem__ method in Inventory class
The Inventory class now consists of a dictionary object with keys being
UPC instances and the values being lists of KitchenItem instances
Created rpki.testing package which will contain unit testing classes
Created testInv module in rpki.testing for unit testing of the Inventory class