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

server/errors.go

@@ -114,6 +114,7 @@ var (
 	errHTTPBadRequestAnonymousCallsNotAllowed        = &errHTTP{40035, http.StatusBadRequest, "invalid request: anonymous phone calls are not allowed", "https://ntfy.sh/docs/publish/#phone-calls", nil}
 	errHTTPBadRequestPhoneNumberVerifyChannelInvalid = &errHTTP{40036, http.StatusBadRequest, "invalid request: verification channel must be 'sms' or 'call'", "https://ntfy.sh/docs/publish/#phone-calls", nil}
 	errHTTPBadRequestDelayNoCall                     = &errHTTP{40037, http.StatusBadRequest, "delayed call notifications are not supported", "", nil}
+	errHTTPBadRequestWebPushSubscriptionInvalid      = &errHTTP{40038, http.StatusBadRequest, "invalid request: web push payload malformed", "", nil}
 	errHTTPNotFound                                  = &errHTTP{40401, http.StatusNotFound, "page not found", "", nil}
 	errHTTPUnauthorized                              = &errHTTP{40101, http.StatusUnauthorized, "unauthorized", "https://ntfy.sh/docs/publish/#authentication", nil}
 	errHTTPForbidden                                 = &errHTTP{40301, http.StatusForbidden, "forbidden", "https://ntfy.sh/docs/publish/#authentication", nil}