Updates from dev branch
This MR includes several updates:
- Option to scale samples w.r.t. background:
ScaleToBkg
- Option to reweight target distribution for regression:
ReweightTargetDist
- Warning if less than 50 events are added from some file -> helps to indicate issues during conversion
- Minor bug fixes
- Improving ROC curve plots -> making them smaller using scikit-learn functions; Also correcting axis labels for ROC curve plots