Added pixel match variables for GsfElectron

Added struct reco::GsfElectron::PixelMatchVariables.
Added relevant getter/setter functions for GsfElectron.
Updated constructors for GsfElectron that take another GsfElectron as
an argument.
Updated class_def.xml to update GsfElectron checksum and add
GsfElectron::PixelMatchVariables.
Updated GsfElectronAglo to add function storing pixel match variables.