Imbalanced classes techniques
http://stackoverflow.com/questions/34655628/how-to-handle-class-imbalance-in-sklearn-random-forests-should-i-use-sample-wei/34661470#34661470
https://github.com/Meena-Mani/SECOM_class_imbalance/blob/master/secomdata_rf.ipynb
http://stackoverflow.com/questions/20463281/how-do-i-solve-overfitting-in-random-forest-of-python-sklearn?rq=1