Notification fixes

* fixed html notifications and test notification button not working anymore due to inline javascript (https://developer.chrome.com/extensions/contentSecurityPolicy.html)
* removed options for html notifications if not available (they are getting removed: https://plus.google.com/+GoogleChromeDevelopers/posts/V8xpT9GgMtT)
* if available, use Rich Notifications API (chrome.notifications) insted of webkitNotifications