Merge pull request #186 from gpetruc/CMGTools-from-CMSSW_7_2_3

Upstream updates from #185
Adding cross section only on MC, and default to 1
replace 'from ROOT.reco import GenParticle' with 'GenParticle = ROOT.reco.GenParticle'
HeppyCore: time report functionality for heppy (run with -t or --timereport to enable)
Pull in some small updates to Heppy
Make photon MC matching optional, as it's quite slow, and switch it off for multilepton for now