Tvheadend

I am assuming developers already use some frequently repeated groups of sub-modules when debugging various aspects of Tvheadend. It would be convenient to have some logging groups so one could quickly enable a pre-defined list of subsystems to include. For example,

descrambling - tbl-csa,descrambler,caclient,csa,capmt,cwc,dvbcam

A fixed set of logging groups would be good to start with, and maybe eventually provide the possibility for users to define their own groups of subsystems