fix for fullscreen indicator bug

Created by: RobertBlackhart

The fullscreenEnabled field tests if the fullscreen abilities are enabled for the browser. This does not change when toggling the button. According to webplatform.org (http://docs.webplatform.org/wiki/tutorials/using_the_full-screen_api#Notification_events) the fullscreenElement can be checked for null to determine if fullscreen is on or off.