Changed the name of the "mvaNonTrig" scale factors to "mvaTrig0p9" and added a
reference.
Added an extra parameter to the "at" function for ElectronSFWeight which tells
it whether to shift the scale factors up or down one sigma; 0 => central value,
+1 => shift up, -1 => shift down.
Added an extra parameter, which can be "up", "down", or "central", which
controls whether the electron scale factors are shifted up or down.
Added the definition for electronSFShift_.
Changed the name of the electronSFID and added the extra parameter that
controls whether the electron scale factors are shifted up or down.