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_score