Add centerOfGeometry, centerOfMass and radius methods on Molecule

[dvermd]

Signed-off-by: dvermd 315743+dvermd@users.noreply.github.com

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Closes: #223

[ghutchis]

This looks good so far. I'd be willing to merge this and merge the best-fit plane as a separate PR.

[dvermd]

I'm happy with this PR been merged and creating another one for the best-fit plane