Generalizes the skeleton_builder function to work with any tracker providing a connection list. Gets tracker info from initialization of the widget in Freemocap rather than hard coding mediapipe values.

Right now, it imports skellytracker just to have a default when running the app stand alone. The standalone app probably isn't used much outside of testing, although because the dependency isn't pinned it shouldn't have any adverse effects.

Also has some other quality of life adjustments I couldn't help but make.

To use the branch of skellytracker this is based on, run pip uninstall skellytracker followed by pip install skellytracker@git+https://github.com/freemocap/skellytracker@philip/flesh_out_mediapipe_model_info