A single button widget for toggling fullscreen mode.
    
| Name | Type | Default | Description | 
|---|---|---|---|
| container | Element | string | The DOM element or ID that will contain the widget. | |
| fullscreenElement | Element | string | document.body | optional The element or id to be placed into fullscreen mode. | 
Throws:
- 
    DeveloperError : Element with id "container" does not exist in the document.
See:
Members
    Gets the parent container.
    Gets the view model.
Methods
    Destroys the widget.  Should be called if permanently
removing the widget from layout.
Returns:
    true if the object has been destroyed, false otherwise.
    
