Added Support for Setting Authorize.net Email Options in Payment Configuration

I have updated ps_authorize.php to allow the Merchant Gateway email options to be set via the Payment Configuration.

The 2 fields that get sent to Authorize.net which I have updated are: x_merchant_email and x_email_customer.

If an email address is sent in x_merchant_email then a message will be sent from the Gateway to that address. There is another setting in Authorize.net (not a VirtueMart setting, but set by logging in to the Authorize.net site) that also sends the Merchant an email. This resulted in the Merchant receiving two messages for every successful order.

The x_email_customer field is simply True or False and is used to configure the Gateway to send an email to the Customer upon successful payment. Again, this was resulting in two messages being sent to the customer because VirtueMart alos sends and email receipt.

Updated ps_authorize.php is attached here and diff file can be found in the BugTracker Task 637: http://virtuemart.net/index.php?option=com_flyspray&do=details&id=637&Itemid=91&option=com_flyspray&Itemid=91