Rename legacy detectors in MCTrackInfo

The MCTrackInfo class is helpful to persist the hit count information from MCHits and the digitisation. Effectively, these are just bit-operations to store many booleans in an unsigned int. That is all fine.

However, the detectors mentioned still refer to the legacy LHCb detector, such as "VeloR" and "VeloPhi". We "abuse" them to store information on the UT, FT and VP, but the names can be confusing. The sooner we fix this, the less work it is, probably :-)