Rich notifications

Now using [chrome.notifications](https://developer.chrome.com/extensions/notifications) API for desktop notifications.

It's worth noting that the Notification Duration option has been removed as a result as we're now offloading notification management entirely to the browser, which already automatically closes notifications after a time.

Finally, I bumped certain build dependencies since I was unable to update the documentation (only done since I removed `notifiication.coffee`).

This PR will fix #204.