Native browser connector for integration with extensions.gnome.org.

A browser extension is needed in order to use it properly:
- Chromium: https://chrome.google.com/webstore/detail/gnome-shell-integration/gphhapmejobijbbhgpjhcjognlahblep
- Firefox: https://addons.mozilla.org/en-US/firefox/addon/gnome-shell-integration/
- Opera: https://addons.opera.com/en/extensions/details/gnome-shell-integration/
- Epiphany: built-in
