Fix iterdays ignoring tzinfo for datetime objects

Also add earliest and latest datetime helpers
Don't call make_app in the dev server
Log double make_app calls w/ traceback
Fix 'indico_scheduler run'
Avoid resetting loggers

Which creates problems with the scheduler's own logger
PEP8 and style fixes
Add room owner on CC for occurrence notifications
Log Janitor delete operations with specific avatar
PEP8