Score normalization redesign

This is the initial redesign of the score-normalization pipeline.

I basically dropped all the old code and made the score normalization stuff as a post-processor where such a post-processor is a BaseEstimator. In such a way, we can leverage Checkpointing and Dasking wrappers avoiding the implementation of custom features.

Furthermore, it will be easier to implement other calibration strategies.

ZNorm is already working and giving the same results as before but with way less code.

Still a WIP, though.

Closes #166 (closed)