minor refactoring, issue 216
refactoring for lighterprints:
- replacing pre_system_daily_tick and post_system_daily_tick with round_started/round_ended signal handlers for issue 216
- move signal receivers into signals.py eventually and add hooks in AppConfig.ready for issue 224

--HG--
extra : amend_source : 781552da0126b33282d6153ab05ed8518adbd39c
s/loglevel/disable_loglevel