WIP: New algorithms to link 'v2' digits/cluster to MCParticle
The actual data is always a relation from CaloCellID -> MCParticle. In case of digits, the cellID of the digit is used. In case of clusters, the cellID of the 'seed' is used.
In addition, there is a CaloHypo2MCParticl which uses the above cluster 'links' to build an 'old' hypo -> MCParticle relation