Cybersource: add processor response message

[dsmcclain]

Cybersource: adds constant for mapping processorResponse to processor error codes.

Note: there is no remote test coverage for the processor response mapping because Cybersource sandbox does not return processorResponse error codes (not that I can find, at least).

Second Note: submitted as a draft PR awaiting further information from Cybersource on whether these processor response messages can be trusted. Do not merge until further notice.

CE-2271

Unit:
5046 tests, 74997 assertions, 0 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
100% passed

Rubocop:
728 files inspected, no offenses detected

Remote:
101 tests, 512 assertions, 7 failures, 0 errors, 0 pendings, 0 omissions, 0 notifications
93.0693% passed

The following tests are failing on master for reasons unrelated to this change:

test_successful_validate_pinless_debit_card
test_successful_tax_calculation
test_successful_pinless_debit_card_purchase
test_successful_authorization_and_failed_capture
 test_successful_asynchronous_adjust
test_successful_3ds_validate_purchase_request
test_successful_3ds_validate_authorize_request

[curiousepic]

Marking this "of interest" before a cleanup of stale PRs