enabled API call for liquidsoap state (enabled & connected streams, enabled & recording recorder, enabled lineins and enabled lineouts)

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.

Origin/aura into master

See merge request autoradio/engine!2

This reverts commit 62a8c7ba, reversing
changes made to a9c94736.

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