Mc stat scaling action

Release notes

Added an Action to SFramework that allows to scale the MC statistical uncertainties of an existing workspace by an arbitrary factor

Details

The action hacks rather deeply into the RooFit internals, manipulating the values of the NLL terms that represent the MC stat. uncertainties. It also modifies all existing snapshots on the workspace. This is needed as otherwise running a fit starting from one of these snapshots would very easily cause numeric problems if the starting value for the MC stat. parameters are too far off their (modified) mean value!