refactor: save and select only max accuracy model

[CaptainJeff]

Updating the Xboost trainers to only save the best model instead of increasingly better outputs. Also adjusted the XGBoost_Runner.py to select the most accurate model from the available models

[bklynate]

@kyleskom - I am curious to know why the model is hardcoded instead of having it be dynamic and selecting the model with the highest accuracy.

[kyleskom]

When I first created this as a project to teach myself ml, that was never a concern to be and was just easy. As the project grew and became some what popular, I never went back to fixing that.