FGO Integration

* Automatic invoice creation - each time a new order is created, the system can automatically create an invoice for the order using FGO service * Automatic action on Order Paid - When an order's payment is captured we can mark the invoice as paid in FGO * Automatic action on Order Cancelled - When an order is cancelled we can automatically cancel or delete the associated invoice * Multiple orders from the same customer can be grouped on one invoice * Support for SAGA integration