Fix ellipsoid jitter

[pjcozzi]

Use GPU RTE

[bagnell]

The EllipsoidPrimitive does not jitter. Here's why:

• The vertex position components are in [-1.0, 1.0] and scaled by the ellipsoid radii. (positions relative to the center of the ellipsoid)
• The model-view and model-view-projection matrices are computed on the CPU with double precision.
• As the distance from the camera to the center of the ellipsoid decreases, the magnitude of the translation of the model-view and model-view-projection matrices decreases.

@pjcozzi Can we close this?

[pjcozzi]

Yes. All good with me. I suspect it could still jitter in some extreme cases with large ellipsoids, but let's wait until it is an actual problem.