Notifications via interface, not only via email

**Describe the solution you'd like**

It would be really helpful to have some kind of notification hub in the WebLate interface to see older and current notifications in one place - maybe in the top right corner next to the profile. This should and could be an addition to the email notifications and it should show a counter for new, unread notifications.

It's somewhat not helpful to only get notified via email and not via the interface. While WebLate is open in a browser it could also show real-time notifications through the browser's system notification functionality.

Hoping, this idea get's picked up and added to WebLate in the future! 👍🏻