build system changes for VDR 1.7.34

for backward-compatibility please use the "master-pre-vdr-1.7.34" branch
added service reference to channel
demuxer: AC3 bsid fixes

- no clue what "srShift" was indented to do
- following the AC3 spec
start streaming when the video stream has been parsed
VDR channels proxy that allows to reorder channels using an external
script or program.
Use XVDRChannels instead of Channels.
Added new configuration parameter to xvdr.conf.
Merge branch 'reorder' of https://github.com/AndreyPavlenko/vdr-plugin-xvdr into master-pre-vdr-1.7.34
use new XVDRChannels in LoadChannelCacheData()