Add ability to use XML and JSON based OMM elements.

[A-j-K]

This is a work-in-progress PR

Description

1. Update old 2008 SGP4 library to the latest 2020 version
2. Add OMM object
3. Add XML OMM reader
4. Add JSON OMM reader
5. Extend existing TLE to allow for XML-based OMM

Fixes #2458

Type of change

• [n/a] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• [n/a] Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update

How Has This Been Tested?

Unit tests will be added to cover some existing code and all new code.

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[A-j-K]

@alex-w CodeFactor failed on imported SGP4 libs. How is this handled? I'm not keen on editing imported code. Can exceptions be added?

[alex-w]

@alex-w CodeFactor failed on imported SGP4 libs. How is this handled? I'm not keen on editing imported code. Can exceptions be added?

See the log - it’s not critical

[gzotti]

Looks like good progress!
For a cleaner history, it's better to occasionally rebase from master, not merge master into your work. This should be very easy if you are editing just a plugin while nobody else interferes.
Codefactor warns about cleaning up empty lines. Please adhere to these. For the "complex method" warnings, if there is no way to reduce complexity, we must accept that.

[alex-w]

Any news?

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.