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

tests/app/dao/test_notification_dao.py

@@ -410,7 +410,7 @@ def test_should_by_able_to_update_status_by_id(sample_template, sample_job, mmg_
         data = _notification_json(sample_template, job_id=sample_job.id, status='sending')
         notification = Notification(**data)
         dao_create_notification(notification)
-        assert notification._status_fkey == 'sending'
+        assert notification.status == 'sending'
 
     assert Notification.query.get(notification.id).status == 'sending'
 
@@ -421,7 +421,7 @@ def test_should_by_able_to_update_status_by_id(sample_template, sample_job, mmg_
     assert updated.updated_at == datetime(2000, 1, 2, 12, 0, 0)
     assert Notification.query.get(notification.id).status == 'delivered'
     assert notification.updated_at == datetime(2000, 1, 2, 12, 0, 0)
-    assert notification._status_fkey == 'delivered'
+    assert notification.status == 'delivered'
 
 
 def test_should_not_update_status_by_id_if_not_sending_and_does_not_update_job(notify_db, notify_db_session):

tests/app/job/test_rest.py

@@ -463,8 +463,6 @@ def test_get_all_notifications_for_job_returns_correct_format(
     assert len(resp['notifications']) == 1
     assert resp['notifications'][0]['id'] == str(sample_notification_with_job.id)
     assert resp['notifications'][0]['status'] == sample_notification_with_job.status
-    assert '_status_fkey' not in resp['notifications'][0]
-    assert '_status_enum' not in resp['notifications'][0]
 
 
 def test_get_job_by_id(notify_api, sample_job):