Show portrait

Shows portrait during VO. Showed when `playSubtitle` is fired, since that happens when the VO is actually being played, and hides on `soundFinished`. As of yet, the images just appear and disappear, but there should be a transition like some crackly fade or stretch from center. @BrettASwift @AmbientOSX 

Needs virtual-world-framework/vwf#245