This includes:
- a new thread to reply to clients using the CASTOR2 protocol (cf.
  stager's RequestReplier).
- a new thread listening to clients coming back to start the transfer.
  This thread polls all outstanding client connections and just accept
  them, so to pass the file descriptor as stdin/out/err to the mover
  (inetd mode).
- a new thread listening to movers for their file close
  operations.
  Details on the implemented protocol in moverhandler.py.
- Extra exposed_ methods to handle the meta-data operations.
  Those replace the stager Job service, which is now obsolete.