Align plane entities with ellipsoid surface

[hpinkos]

Before:

After:

Thanks @bagnell for figuring out the math for this =)

@ggetz can you review?

[cesium-concierge]

Thanks for the pull request @hpinkos!

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[ggetz]

Thanks @hpinkos, will look at this soon.

[ggetz]

Everything looks good, thanks @hpinkos. It is worth re-snapping the Sandcastle thumbnail ?

[hpinkos]

@ggetz updated

[ggetz]

Thanks!