Vibrator API: extract from Navigator

Hi.

The vibrator API's WebIDL [1] should not expose the two methods directly  
in the navigator object.

Instead it should be in a separate interface, so it can be implemented as  
a singleton API in the window/navigator object for a mobile device like a  
phone, or can be implemented on top of the gamepad object whenever the  
gamepad APIs moves forward, to feed vibration back to the controller.

Thanks.

[1] http://dev.w3.org/2009/dap/vibration/