Core UI mixin that all interface subclasses should extend 
 instead of MovieClip for standardized UI initialization.
 
 Note: CoreClip should only be used for classes which will
 extend library clips via linkage id. If you are using 
 ClassUtils to extend a class use
 BaseClip as the onLoad event
 will have fired before the clip is extended.
 
 
public function onLoad():VoidonLoad does core setup when clip registers on stage via onLoad. Do not override this in subclasses; instead override configUI.
Void