Nominalcollision2015 default

- NominalCollision2015 set as default beamspot in ConfigBuilder;
- reco BS updated in run GT's, accordingly ; 
- relvals: NominalCollision2015 used in full SIM postLs1, fast sim postLs1;
               Realistic8TeVCollision used for 8 TeV fast and full sim, all HI wf's 
               (this last: to be updated once reco BS measured)