Add X-REPP-eppcode header to all HTTP responses?

[mwullink]

Do we want a X-REPP-eppcode response header?

pro: quick easy way of getting epp result

con: add uppler protol layer status to http layer

[mwullink]

do not use http header with prefix "X-" this is deprecated.

headers should start with: "REPP-" new header is: REPP-eppcode

only use REPP-eppcode when the http message-body is empty, as is the case with the check command response

[mwullink]

added text for this