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/services_dao.py

@@ -262,8 +262,7 @@ def fetch_todays_total_message_count(service_id):
 def _stats_for_service_query(service_id):
     return db.session.query(
         Notification.notification_type,
-        # see dao_fetch_todays_stats_for_all_services for why we have this label
-        Notification.status.label('status'),
+        Notification.status,
         func.count(Notification.id).label('count')
     ).filter(
         Notification.service_id == service_id,
@@ -281,8 +280,7 @@ def dao_fetch_monthly_historical_stats_by_template_for_service(service_id, year)
     start_date, end_date = get_financial_year(year)
     sq = db.session.query(
         NotificationHistory.template_id,
-        # see dao_fetch_todays_stats_for_all_services for why we have this label
-        NotificationHistory.status.label('status'),
+        NotificationHistory.status,
         month.label('month'),
         func.count().label('count')
     ).filter(
@@ -298,7 +296,7 @@ def dao_fetch_monthly_historical_stats_by_template_for_service(service_id, year)
         Template.id.label('template_id'),
         Template.name,
         Template.template_type,
-        sq.c.status.label('status'),
+        sq.c.status,
         sq.c.count.label('count'),
         sq.c.month
     ).join(
@@ -316,8 +314,7 @@ def dao_fetch_monthly_historical_stats_for_service(service_id, year):
     start_date, end_date = get_financial_year(year)
     rows = db.session.query(
         NotificationHistory.notification_type,
-        # see dao_fetch_todays_stats_for_all_services for why we have this label
-        NotificationHistory.status.label('status'),
+        NotificationHistory.status,
         month,
         func.count(NotificationHistory.id).label('count')
     ).filter(
@@ -356,9 +353,7 @@ def dao_fetch_monthly_historical_stats_for_service(service_id, year):
 def dao_fetch_todays_stats_for_all_services(include_from_test_key=True):
     query = db.session.query(
         Notification.notification_type,
-        # this label is necessary as the column has a different name under the hood (_status_enum / _status_fkey),
-        # if we query the Notification object there is a hybrid property to translate, but here there isn't anything.
-        Notification.status.label('status'),
+        Notification.status,
         Notification.service_id,
         func.count(Notification.id).label('count')
     ).filter(
@@ -388,8 +383,7 @@ def fetch_stats_by_date_range_for_all_services(start_date, end_date, include_fro
 
     query = db.session.query(
         table.notification_type,
-        # see dao_fetch_todays_stats_for_all_services for why we have this label
-        table.status.label('status'),
+        table.status,
         table.service_id,
         func.count(table.id).label('count')
     ).filter(