Getting the data format change (cfr PR 3717) in 72X.

This PR aims at porting in 72X a change in EGamma dataformat related to the electrons mva recording. Essentially mva() naming convention becomes mva_Isolated() for the isolated electrons, which has two advantages. First, it is much easier to browse on git or lxr the places where this method is called, and second, it has permitted to spot all places where gsfElectron.mva() was used, since that method does not exist anymore on the GsfElectron class. These old mva() (previously used to record the "non-isolated" electron mva response) where then changed to mva_e_pi, which is now the unique convention for the soft/non-isolated electron mva.