Adding beta prototype of zero-bin statistical uncertainties in HistFactory, improved HistFactory Navigation, clean-up


git-svn-id: https://root.cern.ch/svn/root/branches/dev/roostats@48437 27541ba8-7e3a-0410-8455-c3a389f83636
Updating HistFactorySchema for new zero-bin statistical uncertainties


git-svn-id: https://root.cern.ch/svn/root/branches/dev/roostats@48438 27541ba8-7e3a-0410-8455-c3a389f83636