tt pythia8 fragment intended for RECODEBUG BTV studies

This  tt pythia8 fragment corresponds to the production of an extra 1 M of RECODEBUG ttbar events for BTV studies (special requests with digi-reco in 72X) that was agreed yesterday at PPD. I just adapted the CSA14 request of pythia8 ttbar to the new guidelines of this campaing (I added the pythia8CommonSettingsBlock and pythia8CUEP8M1SettingsBlock and removed the relevant options included there from processParameters). Also the cross section has been re-evaluated with 10k gen events.