Added pixel match variables to reco::GsfElectron

Added new struct reco::GsfElectron::PixelMatchVariables to hold
variables.
Added setter and getter functions to GsfElectron.
Updated constructors of GsfElectron to copy pixel match variables when
another GsfElectron is passed as an argument.
Updated checksum of GsfElectron in class_def.xml, and added
PixelMatchVariables struct to class_def.xml.
Added method to GsfElectronAlgo to add pixel match information to
GsfElectron.