Remove Notification, NotificationHistory status labels:

Replace labels by adding a key kwarg in the model for status.

We still need this as sqlalchemy attmempts to look for `notification_status`
on the model (Notification/NotificationHistory). To achieve true ORM mapping
(map status -> notification_status) we need the key kwarg.

More here:
http://docs.sqlalchemy.org/en/latest/core/metadata.html#sqlalchemy.schema.Column#key

app/dao/jobs_dao.py

@@ -17,7 +17,7 @@ from app.statsd_decorators import statsd
 def dao_get_notification_outcomes_for_job(service_id, job_id):
     query = db.session.query(
         func.count(NotificationHistory.status).label('count'),
-        NotificationHistory.status.label('status')
+        NotificationHistory.status
     )
 
     return query \