By-passing combine datacards

[anigamova]

While the combine and therefore the datacards are widely used in CMS, there are examples where RooFit workspaces or other stat. model formats are preferred. For analysis preservation purposes, simple combinations, we need tools to convert models to datacards from other possible formats.

• Reverse T2W, i.e. develop a tool mapping a physics model saved within RooFit workspace and combine datacard
• Compatibility with other formats: pyHF
• Standalone tool for analyses using workspaces