Simplify implementation of DTF in FunTuple
To store the output of DTF in FunTuple we now call DecayTreeFitterAlg, which stores a number of quantities from the fit (particleparams, number of fit iterations) in the event store with relation tables linking them to the input particles. It seems simpler to store the 'Fitter' object itself: That requires only a single relation table and would give access to more information, such as status codes, chisquares and the head of the decay tree (the PV in case of a PV-constrained fit).
There may even be a simpler solution: At one time DecayTreeFitter could be called directly from python, see this old twiki page: https://twiki.cern.ch/twiki/bin/view/LHCbBackup/DecayTreeFitter The dictionary is still processed, so I think that this functionality still exists. If FunTuple calls DecayTreeFitter like this, then perhaps no C++ Alg is needed at all.