MEDIUM: cli: handle payload in CLI proxy

MEDIUM: cli: handle payload in CLI proxy

The CLI proxy was not handling payload. To do that, we needed to keep a
connection active on a server and to transfer each new line over that
connection until we receive a empty line.

The CLI proxy handles the payload in the same way that the CLI do it.

Examples:

   $ echo -e "@1;add map #-1 <<\n$(cat data)\n" | socat /tmp/master-socket -

   $ socat /tmp/master-socket readline
   prompt
   master> @1
   25130> add map #-1 <<
   + test test
   + test2 test2
   + test3 test3
   +

   25130>