Remove SHAP dependency

[ReinierKoops]

Problem Description
At the moment we use SHAP. But as we can see here:
https://github.com/shap/shap/blob/master/shap/explainers/_tree.py#L452
SHAP is calling the specific libraries to do the SHAP calculation for them.

If you implement TreeExplainers & Explainer for Classification/Regression manually, it might boost performance and drop our dependency on SHAP (which is kinda messy)

Desired Outcome
Remove SHAP as dependency

Solution Outline
Do as described above

[ReinierKoops]

@PaulZhutovsky thanks for the idea.