Provide a simple way start a decoupled servlet endpoint

Typically, the endpoint address of a decoupled http endpoint is given as a full http URL and the corresponding destination will be set up as a jetty destination. In some cases, where the client is running in a container that has the CXFServlet, it is useful to start a servlet destination using this servlet.

We can provide this option by allowing the endpoint address to be given as a relative path (as used in the servlet destination) and use another runtime property to create the full http URL when setting the WS-A ReplyTo header.