Allow automatically resolving response identities

[glopesdev]

This PR extends the SendResponse operator to automatically resolve response identities when the nested workflow output is a sequence of raw response frames. This extension also provides new overloads to allow more easily building response handlers which are compatible across both Response and Router sockets.

The implementation scans backwards from the request message looking for an empty delimiter frame. If it finds one, it assumes the preceding frames represent the identity of the request, and pushes them to the top of the response message. For simple Response sockets the request does not include any identity frames, and the response frames are routed directly back to the socket.