Automatic binning

Automatic binning
 - added helper functions (purity, stability) + unit tests for them
 - added main script (00_pick_bins.py) + tests

Reorganised tests
 - deleted obsoletes
 - merged tests that belong to one module

Other
- updated binning plots (synchronised with AnalysisSoftware)
- updated rootpy

This pull request is NOT ready to merge. We need to discuss the bug regarding the differences in purity, stability and N events between what is done in the script and what is done in the helper functions.