tpot: Major upgrade

In TPOT 0.4, we've made some major changes to the internals of TPOT. We've summarized the changes below. Added new sklearn models and preprocessors AdaBoostClassifier BernoulliNB ExtraTreesClassifier GaussianNB MultinomialNB LinearSVC PassiveAggressiveClassifier GradientBoostingClassifier RBFSampler FastICA FeatureAgglomeration Nystroem Added operator that inserts virtual features for the count of features with values of zero Removed XGBoost as a dependency Too many users were having install issues with XGBoost Replaced with scikit-learn's GradientBoostingClassifier Improved descriptiveness of TPOT command line parameter documentation Removed min/max/avg details during fit() when verbosity > 1 Replaced with tqdm progress bar Added tqdm as a dependency Added fit_predict() convenience function Added get_params() function so TPOT can operate in scikit-learn's cross_val_scor