Celery tasks for find, dl, parse, save

Added celery tasks to find match ids of accessible leagues that aren't
already parsed, look up the match replay urls from the matchurls tool
(assumed to be running on localhost:3100), download the replay, parse it
into mongodb, then delete the replay. Make sure to update
celeryconfig.py, then start workers with
    celery multi start 1 --app=alacrity.mq -l debug -B
This starts 1 worker as a daemon, outputting log info at the debug level
and also running celery beat for scheduling (the -B flag).