notifications: make update alerts non-persistent

once acked, they remain acked. no need to keep nagging the user about them.

src/routes/test/notifications-test.js

@@ -19,7 +19,7 @@ describe('Notifications API', function () {
 
     it('can add notifications', async function () {
         for (let i = 0; i < 3; i++) {
-            const id = await notifications._add(null, `title ${i}`, `message ${i}`);
+            const id = await notifications._add(`title ${i}`, `message ${i}`, { eventId: null });
             notificationIds.push(id);
         }
     });