Enhancements for validation of DB urls

We now turn off retries and DB pooling, and make sure to always close the connection

data/model/notification.py

@@ -1,5 +1,7 @@
 import json
 
+from peewee import SQL
+
 from data.database import (Notification, NotificationKind, User, Team, TeamMember, TeamRole,
                            RepositoryNotification, ExternalNotificationEvent, Repository,
                            ExternalNotificationMethod, Namespace, db_for_update)
@@ -82,7 +84,6 @@ def list_notifications(user, kind_name=None, id_filter=None, include_dismissed=F
   elif limit:
     query = query.limit(limit)
 
-  from peewee import SQL
   return query.order_by(SQL('cd desc'))