Star map star backend

[alexanderson1993]

Description

Depends on #209 - Don't review until that is merged.

Adds the classes and inputs for creating, updating, and deleting stars. Also includes a simplified function which can turn the satellite properties of an object into cartesian (XYZ) coordinates.

Related Issue

Closes #174
Closes #175

How do you know the changes work correctly?

Added automated tests.

Types of changes

• Docs Change (changes were only made to documentation)
• Refactor (non-breaking change which improves code)
• 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)

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the built-in project documentation.
• My change adds dependencies to this project.
• I have added tests to cover my changes.
• All new and existing tests passed.

[tannerchamb]

Everything looks good to me! The tests pass fine and I don't see any issues.