Add hard vertex selection tool
This MR adds a new tool to TrkVertexWeightCalculators package providing a tool to classify primary vertices, between hard and pileup, using a BDT presented and trained by @driva here: https://indico.cern.ch/event/1345645/#2-bdt-based-hard-scatter-selec. The tool is able to use also electrons as input.
The tool uses IVertexWeightCalculator as an interface, as proposed by @jburzyns
To run the example this ROOT file must be placed in the data directory: https://cernbox.cern.ch/s/4N20Ueaq9qHI56i (it will be copied to groupdata)
Edited by Ruggero Turra