Move DAO function for new platform stats page

Moved the `fetch_new_aggregate_stats_by_date_range_for_all_services`
DAO function from the services DAO to the Notifications DAO since this
function queries the `notification` and `notification_history` tables.

Also added a test to check that the data returned from the function
takes BST into account.

app/dao/notifications_dao.py

@@ -609,3 +609,31 @@ def guess_notification_type(search_term):
         return EMAIL_TYPE
     else:
         return SMS_TYPE
+
+
+@statsd(namespace='dao')
+def fetch_new_aggregate_stats_by_date_range_for_all_services(start_date, end_date):
+    start_date = get_london_midnight_in_utc(start_date)
+    end_date = get_london_midnight_in_utc(end_date + timedelta(days=1))
+    table = NotificationHistory
+
+    if start_date >= datetime.utcnow() - timedelta(days=7):
+        table = Notification
+
+    query = db.session.query(
+        table.notification_type,
+        table.status,
+        table.key_type,
+        func.count(table.id).label('count')
+    ).filter(
+        table.created_at >= start_date,
+        table.created_at < end_date
+    ).group_by(
+        table.notification_type,
+        table.key_type,
+        table.status
+    ).order_by(
+        table.notification_type,
+    )
+
+    return query.all()