Comparison of multiple models in evaluator plots & metrics

[JanBenisek]

When the user builds multiple different models, it would be handy to evaluate them in the same time. This means that the plotting functions:

• evaluator.plot_roc_curve()
• evaluator.plot_confusion_matrix()
• evaluator.plot_cumulative_gains()
• evaluator.plot_lift_curve()
• evaluator.plot_cumulative_response_curve()

would have the possibility to add results from multiple models.