make backend.py a daemon

[lost-tty]

Making backend.py a daemon will make additional feature (e.g. gluon-announced support) a lot easier.

[mweinelt]

I don't think t his will be necessary, as with gluon-announced ffmap-backend could become just a client to it. My current implementation sets a socket timeout and, when no results have been received for that duration, will return the received data.