Lightspeed R-series: Credit Card Fee Item par AdVision eCommerce

Extension is activated on the open sale (register) interface of Lightspeed Retail R-series admin (https://us.merchantos.com/register.php). Below "Payment" button, "Credit Card Fee" button is shown. When button is clicked:

- if CC Fee item is already a sale line on sale, extension will remove it (so button can be clicked to remove fee)
- if CC Fee item is not already a sale line, extension will get "Credit Card Fee" item details, use price of item to calculate fee amount, and add item as sale line with price set to fee amount; e.g. if CC Fee item is $4, fee percentage = 4%, a sale with total = $200 would have a CC Fee of $8 (4% of $200)