Decouple mailing/broadcasting from Celery

[DonDebonair]

Currently mailing reports is tightly coupled with Celery, even allowing for an async switch, which doesn't seem all that useful in a CLI context. Mailing should be decoupled from scheduling and put into its own package probably. This package (broadcasting?) could form the basis of a pluggable broadcasting system (mail, slack, etc., see #3 ).
Celery must be optional. process_job should invoke another function that does the heavy lifting and is decoupled from Celery.