fix(service-worker): Open notifications if no status (#1378)

* fix(service-worker): Open notifications if no status

If the notifications couldn't be fetched fallback to displaying all notifications (aligned with how the Mastodon Web UI [handles it](https://github.com/tootsuite/mastodon/blob/master/app/javascript/mastodon/service_worker/web_push_notifications.js#L118)).

Might fix https://github.com/nolanlawson/pinafore/issues/1365.

* fix(service-worker): Use self

src/service-worker.js

@@ -128,7 +128,10 @@ self.addEventListener('push', event => {
 async function showSimpleNotification (data) {
   await self.registration.showNotification(data.title, {
     icon: data.icon,
-    body: data.body
+    body: data.body,
+    data: {
+      url: `${self.origin}/notifications`
+    }
   })
 }