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/public/config.js

@@ -7,7 +7,7 @@
 
 var config = {
   base_url: window.location.origin, // Change to test against a different server
-  app_root: "/app",
+  app_root: "/",
   enable_login: true,
   enable_signup: true,
   enable_payments: false,