Updated SDSBlender to Blender 2.54

I have finally updated the SDS/Blender plugin. It took a couple of days to chase down all the API changes between Blender versions 2.52 and 2.54, but the plugin now works. Apart from being more stable, Blender 2.54, now supports primitive_uv_sphere_add which means that I can now programmatically generate cell-based views of the SDS organisms. I also added tetrahedra importing. :)