[MRG] preprocessing.normalize_proba

Deprecated the HMM.normalize and instead used preprocessing.normalize_proba.
Changed the usage of normalizations across the code to instead use preprocessing.normalize_proba.
All tests passes, didn't manage to get the benchmark to work properly so I don't know the performance impact.

In response to: https://github.com/scikit-learn/scikit-learn/issues/1862

Not sure about the name adopted it from predict_proba