#485 - Fix some compilation problems on a few tests, minor updates to docs in a few places
#485 - Add a ‘confirmed’ flag to payment transaction
#485 - Change the map of additional fields on payment transaction to String -> Serializable
#485 - Fill out anonymous customer information from the gateway
#485 - Only mark payments as invalid for the current gateway if it does not support multiple payments per order
#485 - Set the payment type according to what was set from the gateway response
#485 - Populate billing address fields on the order payment from the gateway response
#485 - Fill out the additional fields map onto a payment transaction from the response DTO
#485 - Implement mark payment as invalid and checkout initiation in the default gateway checkout service