introduce NominalCollision2015 beamspot scenario, according to: https://indico.cern.ch/event/341218/; relvals as well as VtxSmearedDefaultKey not modified
properly initialize event attributes in pythia8 lhe interface
update key configuration snippets for pythia 8.2 and create organized fragments for common pythia8 settings
improve comment in config file
proper accounting for merging weights from CKKWL, UMEPS, UNLOPS
codes necessary to fix computation of cross sections
codes necessary to fix computation of cross sections
Merge pull request #5578 from franzoni/beamspot_NominalCollision2015-CMSSW_7_3_X_2014-09-25-0200

introduce NominalCollision2015 beamspot scenario,
Merge pull request #5601 from syuvivida/73x_fixXSec_eiko

GeneratorInterface -- Codes that fix the cross section computation
Merge pull request #5590 from bendavid/pythia82fixes

Some fixes and configuration updates for Pythia 8
Merge remote branch 'origin/CMSSW_7_3_X' into CMSSW_7_0_X