Updates after review

- Modified the services_dao to return an int instead of a datetime to
make usage easier and removed the BST function on year as it is not
relevant for year
- Improved tests do there is less logic by ordering the result so there
is less reliance on the template id
- Renamed variable in stats_template_usage_by_month_dao.py to make it
consistent with the method

app/dao/stats_template_usage_by_month_dao.py

@@ -15,10 +15,10 @@ def insert_or_update_stats_for_template(template_id, month, year, count):
         }
     )
     if result == 0:
-        new_sms_sender = StatsTemplateUsageByMonth(
+        monthly_stats = StatsTemplateUsageByMonth(
             template_id=template_id,
             month=month,
             year=year,
             count=count
         )
-        db.session.add(new_sms_sender)
+        db.session.add(monthly_stats)