Switch data cash tests from deprecated DataCashGateway#credit to #refund

If #credit is being used with a credit card rather than a ca_reference
as an argument then we cannot migrate - These tests will break when the
\#credit method is removed
Fix failing data cash remote unsuccessful capture test
Add functionality to enable card pre registration with data cash

Conflicts:
	lib/active_merchant/billing/gateways/data_cash.rb