#817 Use celery to queue SMS messages for delivery.
#817 Turn bb_mail_sender into a celery worker.
#817 Update bb_mail_sender so that it outputs something to the console. This is so that I can see it has processed the task in the celery worker.
#817 Convert sms_sp to a celery worker.
#817 Update bb_notification_handler so that it uses celery to queue an email, rather than sending synchronously.
#817 Added print lines so that they show up on the celery worker.
#817 Update the method in sms_sp module to use .delay so that I don't have to update each method where it is currently called.
#817 Turn print line into a log.debug as no longer needed to print onto the console.
#817 Refactor send_sms methods.
#817 Add log.debug lines to represent the notifications being put in the background queue.
#817 Rename method for queueing mail notifications.
Move log stuff around a bit. Don't know why. Probably broken it now for a pointless change.
Merge branch 'feature/#817-Implement_Message_Queueing_for_sending_emails' into develop