Add support for DVB/Fastscan/Freesat/BSkyB bouquets

This is an attempt to integrate the bouquets to tvheadend. Actually, the code allows automatic channel management and user-defined channel number offsets per bouquet. Also, a channel tag might be created for the bouquet.

Please, report any issues here before merge to the main tvheadend tree.

EDIT: To select BSkyB region use TVHEADEND_BSKYB_REGIONID environment variable. The filter is set to 1 (London) by default. There is too much bouquets and I don't think that it's good to push them all to bouquet tables.