Allow for optional response messages

[mwullink]

Make response handling more easy.

For commands that return only a basic response containing a clTRID,svTRID and result code, this response can be replaced by 3 http response headers.

then server does need to generate json/xml and client does not need to parse response

if the client does prefer the response message, the server must support a query string param to enable full responses?

example basic request

   S:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   S:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   S:  <response>
   S:    <result code="1000">
   S:      <msg>Command completed successfully</msg>
   S:    </result>
   S:    <trID>
   S:      <clTRID>ABC-12346</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp> 

[mwullink]

Added optional responses where the OK response consists out of only the result code and the transaction ids. the response must stay optional because in case of an error an error response must be sent