Added a test scenes ("Test All...") button to the Scene Dialog. When pressed,...

Added a test scenes ("Test All...") button to the Scene Dialog.  When pressed, all scenes in the current scene file are displayed and images of the graphics region are captured.  Next, a dialog is displayed that shows, on the left, the preview image from the scene and on the right, a image of the graphics region from display of the scene.  If the images do not match, there may be a problem with the scene.