Mean motion based propagation from Python

[ChristopherRabotin]

Effects

Python mission design now has a two_body function that computes the true anomaly of this orbit at some other epoch using the mean motion. This function will compute it for N objects in parallel.

For a single orbit, just call at_epoch(new_epoch) on the Orbit structure, and it will return a copy of that orbit at the new epoch.

This also renames the elevation_of function to azimuth_elevation_of and returns the azimuth data too.

If this is a new feature or a bug fix ...

• Yes, the branch I'm proposing to merge is called issue-xyz where xyz is the number of the issue.

If this change adds or modifies a validation case

• No.

[github-actions]

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