Support for ThOr functor in FunTuple

This MR contains:

• Support for ThOr functor in FunTuple.
• Added two tests (here and here) of nTupling with LoKi and ThOr (with LHCb::Particles and LHCb::MCParticles).
• Other small additions include: nTupling of all (multiple) candidates in an event, moving the python helper classes and functions (ParticleTupleProp and convert_to_parsable_objs) central and better naming of Gaudi::Property objects.

This MR depends on Rec!2420 (merged) and Phys!930 (merged).

Work on DPA task https://gitlab.cern.ch/lhcb-dpa/project/-/issues/6.

FYI: @powen and @mferrill .