setup H->gg bias measure in xsec.py and fitBiasStud.py

  xsec.py: bias numbers for Group 3 (including bernstein) biases
  singleUseScripts/biasEnvelope.py setup to read in Hgg-style bias file
added func helpers.py:copyTreeBranchToNewNameTree
Merge pull request #6 from jhugon/bakToHggBiasMeasure

Bak to hgg bias measure