DecayTreeFitterAlg - Needs modernising to support DD4HEP

See discussion in DaVinci#65 (closed)

DecayTreeFitterAlg  FATAL DecayTreeFitterAlg:: Exception throw: get():: No valid data at '/world:DetElement-Info-IOV' StatusCode=FAILURE

Component needs to be completely modernised to support dd4hep.

@pkoppenb @erodrigu FYI - Currently assigned it to you, but expect you will reassign to whomever maintains this now.