reactivated fallback and callback from lqs, fixed multiple lineins on engine level, having the problem that fallback does not start

5 different recorders possible. 'last' missing thing on liquidsoap side: smooth transition between mixer.selects

recording is now part of engine.liq. a redefinition of the recorded source is needed if those two should be separated.

several things: critical socket threading bug from comba resolved. adapted interfaces to pv / tank / database

code quality enhanced, timer management improved, started to implement methods for manual playlist editing