add functors to get LHCbIDs and Nhits on VELO sides

Add functors to access LHCbIDs, HitPattern and number of hits on a VELO side.
The LHCbID functor is based on work by @lcalefic
Note that I'm only testing these in track selections and not in DaVinci, for which additional work might be needed.

Suggestion for improvements are very welcome!