Add the flag fromPV to PrChecker

A new flag fromPV is added to select the tracks directly from PV.

The option file for testing the new feature is attached: PrCheckerEfficiencyPlots_HLT2.py. To run this option file:

BrunelDev_HEAD/run gaudirun.py PrCheckerEfficiencyPlots_HLT2.py 

In the outputfile: PrCheckerPlots_HLT2.root, the histograms with the label of fromPV can be generated.

I'd appreciate it if you could let me know when the WIP lable can be removed. Thanks!