Draft: Added converters for new cluster formats (which can be packed)
Adds the surrounding machinery to convert between different types of clusters (including VPMicroCluster, VPLightCluster).
In addition, fixes the missing setting of the fractionx, and fractiony in the converter of PRVPHits to VPLightClusters (@ahennequ)
Requires LHCb!4287 (closed) and Moore!2670 (closed)
Edited by Laurent Dufour