variables for shop item properties#661

ex. {item_price:cake} would get the price of the “cake” item, {item_stock:cake} would get the remaining stock of the “cake” item, {item_addedrole:} for the role that the item adds when used, etc.

this feature would be useful in making a .sell ar, since currently we have to make a new ar for every refundable item in the shop