[Global] Rewrite algorithm to dataset based

[pierrenodet]

At the moment, Bagging and Boosting (not Stacking and GBM) are using rdd in order to batch data or compute current prediction error and a new dataset is created to be passed to the weak learner.

The issue is that the metadata is not passed and is lost. That's an issue for datasets that relies on them.

[pierrenodet]

solved by #27