v0.8.0 - web share and web push

New stuff:

Chat groups now can deliver Web Push notifications to offline users. Requires valid VAPID keys, not easy to generate, but easy enough to configure - three parameters to application.properties.

Creating a private world now utilizes Web Share API, makes it easy to share the world URL and invite friends.
World URL is also shared in the active chat log, whatever is active at the moment.

New REST API endpoint to attach persistent custom user data to user object.

And long time coming, server capabilities endpoint.

Release video: https://youtu.be/kHUOjqwS0ns