First pass updating the volume rendering to optix only.

Creation of the element traversal function.
First working all-optix volume rendering.  Only supports simple riemann.  Additionl integration methods and better interaction with the gui remains to be added.
Fixed crashes relating to the cuda module.  Now crashes during isosurface generation.
Removed all reference of cuda from the code.  Cut surfaces still work, but volume rendering doesn't, and isosurfaces still cause the display driver to reset.
Isosurface module cleanup.
Fixed isosurface bugs.  Now volume rendering and isosurfaces can't be executed in the same session.
Fixed crash when trying to use isosurfaces and volume rendering in the same session.