Merge branch 'master' into refactor-send-tasks-into-shared-code

Conflicts:
	app/celery/provider_tasks.py
	tests/app/celery/test_provider_tasks.py

app/delivery/send_to_providers.py

@@ -79,6 +79,7 @@ def send_email_to_provider(notification):
             send_email_response.apply_async(
                 (provider.get_name(), reference, notification.to), queue='research-mode'
             )
+            notification.billable_units = 0
         else:
             from_address = '"{}" <{}@{}>'.format(service.name, service.email_from,
                                                  current_app.config['NOTIFY_EMAIL_DOMAIN'])