Improved frontend handling.

Frontend now remains open at all times, with signal lock, snr & signal level
polled from Interupt.

Updated driver for DM04/QQBOX USB DVB-S BOXES to version 1.70.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>