Widget-Parent is an extension designed to be used with Base.build, to create
widget classes which can manage nested child widgets.

For example, it could be used to create Menu widgets, which contain MenuItem 
widgets, or Tree widgets, which contain TreeNode widgets.

3.1.1

* No changes

3.1.0

*   "childAdded" event renamed to "addChild"
*   "childRemoved" event renamed to "removeChild"
*   Now augmented with Y.ArrayList
*   "selection" attribute now returns an Y.ArrayList or Widget
*   Removed "children" attribute since that functionality is provided 
    by Y.ArrayList
	-  Can retrieve # of child via the size() method
	-  Can iterate children via this.each()
	-  Can retrieve a individual child via the item() method
* add method will always return a Y.ArrayList instance for easy chaining
* removeAll method will always return a Y.ArrayList instance for easy chaining
* added selectAll() and deselectAll() methods
* widget UI will render children added/inserted children after widget is rendered
* widget UI will update when a child is removed
