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

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

Origin/aura into master

See merge request autoradio/engine!2

# Conflicts:
#   libraries/database/broadcasts.py
#   libraries/security/user.py
#   libraries/security/whitelist.py

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