TextBox and TextGraphic now call applyDisplayObjectProperties() at the end of their draw() method, like all other GraphicElements. This method handles setting the visibiliy of the GraphicElement's DisplayObject, among other things.
Note: We should make it unnecessary for each GraphicElement subclass to have to call applyDisplayObjectProperties() at the end of draw(). The GraphicElement base class should ensure that this gets called at the appropriate time.
Group now calls draw() on graphic elements even if they are invisible, because otherwise applyDisplayObjectProperties() never gets called and the TextLines stay visible. Group was assuming that the only visible stuff in a GraphicElement is drawn with Graphics calls, which isn't the case.
This change is OK for now because every GraphicElement currently has its own DisplayObject, but it will need to be rethought when GraphicElements share DisplayObjects.
Bug: MXMLG-206 ("Setting visible property on TextGraphic does nothing")
QA: Peter, please add a Mustella test case for the 'visible property of TextBox and TextGraphic