Closes #397

     Add feature detection for -ms-device-fixed positioning. If it doesn't exits, IHM handling logic should fall back to the more archaic logic in Windows 8,
     (calculating the offsets between the  top and bottom of the visual viewport from the top and bottom of the layout viewport)
     in order to maintain the illusion that position fixed elements (AppBar and Flyout) are positioned relative to the visual viewport and not the layout viewport itself.