Added support HTC 2.0 theory

[alex-w]

Description

Added support HTC 2.0 theory for compute positions of 3 moons of Saturn: Helene, Telesto and Calypso

Type of change

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

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
• 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

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching src/**/*.cpp:

• Are possibly unused includes removed?

This is an automatically generated QA checklist based on modified files

[gzotti]

Great!
Move to Calypso, center Saturn, and see Tethys fixed in the West. :-)
On Telesto, Tethys is fixed in hour angle 21h.
On Helene, Dione does the same.

Apart from the cosmetics, I think it's fine.