Server and Direct: delivery address is mandatory

[judgej]

Most gateways do not have a mandatory delivery address, but Sage Pay does when registering a transaction. For consistency, this driver should protect the application from that inconsistency.

I propose that a missing delivery address is automatically populated from the billing address. To reduce BC breaks, this should probably be an option that can be set at the gateway level, defaulting to off.

[judgej]

Rather than setting the delivery address the same as the billing address if it is empty, a single flag to explicitly copy it across should be used - but the control entirely in the hands of the merchant site. Maybe something like shippingAsBilling.

[judgej]

Released as 3.2.0