Scikit-learn API enhancements

[weixuanfu]

Below are some ideas for future enhancements for pennaipy:

• refine default values of parameters in PennAI for better AutoML application
• support more classifiers and regressors in the PennAI configurations
• update knowledgebase every half year or quarter based on latest version of scikit-learn/xgboost
• Add support of cuML for big data analysis with GPU (similar with TPOT cuML)