Add seed to explainer + remove np.random.state()

[ReinierKoops]

Problem Description
Currently we have a np.random.seed state set in the code somewhere. Now that SHAP has the ability to set seed for its tree explainers, we can remove that code and add the seed directly to SHAP explainer.

Desired Outcome
Do the problem described above.

Solution Outline
Remove it and add random state reference as seed to explainers.

[ReinierKoops]

fixed in PR #252