Mercury gateway updates

These are changes to the Mercury Gateway needed to pass a recent Mercury integration certification.   The Mercury Developer Integrations representative I worked with for the certification was Michael Mantineo, mmantineo@mercurypay.com.  The changes included in this PR are:

    * when parsing mercury response if ref_no is not present use invoice_no for ref_no

    * include AcqRefData for PreAuthCapture as well as reversal

    * default to partial auth deny
Hi @andrewpaliga, In order to successfully process some of the transactions which where required as part of the mercury integration certification we where required to use the :invoice_no parameter from the mercury gateway response as :ref_no in subsequent requests.

Would allowing for the specification of :ref_no through transaction options help the tests get around this logic? https://github.com/shulmang/active_merchant/compare/mercury_gateway_commit_options?expand=1