Use Binding and Current.State dictionary for data passing on Inventory/Add Item pages

Tasks addressed:
 - **595-73**: Improve navigation/data passing between pages
 - **595-52**: Tweak "Add New Item" Page: Keyboard for "Quantity" Field
 - **595-62**: Navigate back to shopping list panorama item after adding new shopping list item
 - **595-59**: Modify Backstack upon returning from AddNewItem page

Very important: also added quantity amount/type to the FoodItem database, so a UPC is now associated with a specific amount of the food item.