Offer alternative ways of reporting missing bus messages

[abompard]

Currently the verify_missing command only prints missing message to the log.
It would be nice to be able to send them via email too.

[jeremycline]

I think we can hook it up with https://docs.python.org/3/library/logging.handlers.html#smtphandler, it should be as simple as adding a new handler to the logging configuration.