Important JER fix (from jpata/fixes_march29 base)

[d-salerno]

Important JER fix that:

• adds stochastic smearing to unmatched jets so that they have a non-zero JER correction.
• updates JER scale factors to latest.

based off https://github.com/jpata/cmssw/tree/vhbbHeppy80X_heppy_fixes_march29, so also includes changes from there...