Implement sans-gui application variant

[tsalemink]

Feature Request

Feature Description
Implement a sans-gui variant of the application.

Use Case
To integrate this application into existing workflows.

Additional Context
The following information will need to be passed in as command line arguments instead of being defined in the GUI:

• Marker set,
• Input directory,
• Output directory,
• Anthropometric measurements (combined CSV file?),
• Enable knee-axis-optimisation (optional).