Feature : Shopping List

[Pythyu]

New feature : Shopping List from #20.

• Ability to right click on items to add the shopping list.
• Items are stored into a "Shopping List" window with 4 columns. The item name, the cheapest price per unit of the item, the world and an action where you can remove items from the shopping list.

As always, if you feel it's missing something or something is wrong, don't be shy to let me know :)