LAO slides have no effect on image quality

[aylward]

Changing the slide has no noticeable effect on the rendering quality or speed.

Also, sometimes moving one slider causes the other to move into unpredictable new values.

[floryst]

From a prior discussion, we intend to have LAO be an optional slider that enables ambient occlusion on top of volumetric blending.

Additionally, this is related to #277.

[aylward]

@aylward - verify on volview-dev.kitware.app

[sankhesh]

@aylward There are no LAO sliders on the app anymore.