Add VPRetinaClusterCreator and option to run it in the VP sequence (default False)
Added also a RawEventSimpleCombiner to add RetinaCluster to the RawEvent:
VPRetinaClusterCreator creates a RawEvent in LHCb::RawEventLocation::VeloCluster because default RawEvent is const.
RawEventSimpleCombiner combines the two RawEvents.
It requires that LHCb!2436 (merged) is merged
Add VPRetinaClusterCreator to Boole is an explicit request from VeLo-RTA joint meeting