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

cmd/web_push.go

@@ -0,0 +1,39 @@
+//go:build !noserver
+
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/SherClockHolmes/webpush-go"
+	"github.com/urfave/cli/v2"
+)
+
+func init() {
+	commands = append(commands, cmdWebPush)
+}
+
+var cmdWebPush = &cli.Command{
+	Name:      "web-push-keys",
+	Usage:     "Generate web push VAPID keys",
+	UsageText: "ntfy web-push-keys",
+	Category:  categoryServer,
+	Action:    generateWebPushKeys,
+}
+
+func generateWebPushKeys(c *cli.Context) error {
+	privateKey, publicKey, err := webpush.GenerateVAPIDKeys()
+	if err != nil {
+		return err
+	}
+
+	fmt.Fprintf(c.App.ErrWriter, `Add the following lines to your config file:
+web-push-enabled: true
+web-push-public-key: %s
+web-push-private-key: %s
+web-push-subscriptions-file: <filename>
+web-push-email-address: <email address>
+`, publicKey, privateKey)
+
+	return nil
+}