Support Web Push Notification with VAPID

### Your use case

#### What would you like to do?
Wake up sleeping Browser Tabs or closed Element-Web tabs on new Messages

#### Why would you like to do it?
Missing Messages if tab is closed (or to many tabs run and browser put element to sleep).

#### How would you like to achieve it?
Using WebPushNotification with VAPID

### Have you considered any alternatives?

Bringing hydrogen-web to a more featured state (and complete device encryption handshakes).

### Additional context

Works with Chrome based Browser, Opera and Firefox (not with Safari):
https://developer.mozilla.org/en-US/docs/Web/API/Push_API