Engine core refactoring with improved scheduling.

aura.py

configuration/sample.engine.ini

guru.py

libraries/database/broadcasts.py

meta.py

modules/base/enum.py

modules/base/exceptions.py

modules/cli_tool/padavan.py

modules/communication/liquidsoap/communicator.py

modules/communication/liquidsoap/playerclient.py

modules/communication/redis/adapter.py

modules/communication/redis/messenger.py

modules/core/startup.py

modules/core/state.py

modules/liquidsoap/engine.liq

modules/liquidsoap/fallback.liq

modules/liquidsoap/in_filesystem.liq

modules/scheduling/scheduler.py