Add PWA, service worker and Web Push

- Use new notification request/opt-in flow for push
- Implement unsubscribing
- Implement muting
- Implement emojis in title
- Add iOS specific PWA warning
- Don’t use websockets when web push is enabled
- Fix duplicate notifications
- Implement default web push setting
- Implement changing subscription type
- Implement web push subscription refresh
- Implement web push notification click

web/src/app/WebPushWorker.js

@@ -0,0 +1,46 @@
+import notifier from "./Notifier";
+import subscriptionManager from "./SubscriptionManager";
+
+const onMessage = () => {
+  notifier.playSound();
+};
+
+const delayMillis = 2000; // 2 seconds
+const intervalMillis = 300000; // 5 minutes
+
+class WebPushWorker {
+  constructor() {
+    this.timer = null;
+  }
+
+  startWorker() {
+    if (this.timer !== null) {
+      return;
+    }
+
+    this.timer = setInterval(() => this.updateSubscriptions(), intervalMillis);
+    setTimeout(() => this.updateSubscriptions(), delayMillis);
+
+    this.broadcastChannel = new BroadcastChannel("web-push-broadcast");
+    this.broadcastChannel.addEventListener("message", onMessage);
+  }
+
+  stopWorker() {
+    clearTimeout(this.timer);
+
+    this.broadcastChannel.removeEventListener("message", onMessage);
+    this.broadcastChannel.close();
+  }
+
+  async updateSubscriptions() {
+    try {
+      console.log("[WebPushBroadcastListener] Refreshing web push subscriptions");
+
+      await subscriptionManager.refreshWebPushSubscriptions();
+    } catch (e) {
+      console.error("[WebPushBroadcastListener] Error refreshing web push subscriptions", e);
+    }
+  }
+}
+
+export default new WebPushWorker();