2.3.1 preparation
CC-5004: Fix mistake in api_client.cfg

-first let's remove the mistake...
CC-5001: remove /etc/monit/conf.d/monit-airtime-rabbitmq-server.cfg on 2.3.1 upgrade

-fixed
refactor some liquidsoap code + remove unused --data argument
CC-4976: Cannot select Ogg/Vorbis output stream after selecting SHOUTcast then selecting Icecast

-fixed
CC-5005: airtime-purge doesn't remove all files
CC-5005: airtime-purge doesn't remove all files

-cleanup
CC-4993: airtime-check-system reports airtime-liquidsoap as down

-fixed
Merge branch '2.3.x' into devel