feat: service worker updates: display unrecoverable state event

refs #604

src/app/services/service-worker-update.service.ts

@@ -32,5 +32,8 @@ export class ServiceWorkerUpdateService {
                     break;
             }
         });
+        swUpdate.unrecoverable.subscribe(event => {
+            notificationService.notify("SwUpdate: unrecoverable state. Reason=" + event.reason + ", type=" + event.type, 10000);
+        });
     }
 }