dvdplayer: add a clock sync stream type

This can be used to let input stream control the playback speed of dvdplayer
and for example keep multiple xbmc instances in synchronous playback.

Currently a psuevdo codec called BXA is used (based on the airtunes stream)
which passes a CurrentHostCounter() tick at which point the pts of the
packet is supposed to be heard/seen.
airtunes: make sure shairplay deintializes on shutdown
libshairplay: split configured from installed state (DROP WHEN FINAL)
libshairplay: always build in debug (DROP WHEN FINAL)
airtunes: let shairport/shairplay use same session handling
airtunes: extend BXA format to pass block header with timestamp

This allow us to pass other types of packets through the pipe.
airtunes: send airtunes to dvdplayer
airtunes: support newer libshairplay with clock sync support

This provide a clock stream whith the time that sound is expected
to be heard from speakers to keep multiple units synchronized.
airtunes: move CSession into cpp file

It doesn't need to be global so put it in private namespace
airtunes: re-open player on flush requests

Thus make xbmc react directly on pause/track change and such
airtunes. bxa demuxer should not abort input stream on start
wip: force silence for dvdplayer audio on startup