addition of soft electron mva, after fixing #4565 merge conflicts

Change in GsfElectron data format:
- rename old mva variable with mva_e_pi
- add mva_Isolated

This PR just picks what's in #4565 and adds a fix to merge conflict in merging PhysicsTools/SelectorUtils/interface/PFElectronSelector.h
a3409cd is applied on top of CMSSW_7_2_X_2014-07-30-0200
and only PFElectronSelector was touched