First_data gateway integration test is working, even if it is a bity hacky

just minor grammatical changes to the error message

more gateway tests working

Fix avs result codes in first_data class

Unit tests, all passing tests pass, failing tests not handled gracefully yet. \n5 tests, 11 assertions, 1 failures, 2 errors, 0 skips

added a few more changes FD gateway seems to throw a currency error not only during but also after an unsuccessful transaction when sent nil creditcard nodes

dry it out