Store hits indices in Pr::Tracks
Change PrForwardTracks to PrLongTracks to make it adaptable for both Forward tracks and match tracks;
Add hits indices ft_index, vp_index and ut_index, nFTHits, nUTHits, nVPHits to PrLongTracks.h;
Add hits indices vp_index and ut_index, nUTHits, nVPHits to PrUpstreamTracks.h;
Change hit to vp_index and add lhcbID in PrVeloTracks.h for consistency;
Adapt 'PrFittedForwardTracks.h' and PrIterableFittedForwardTracks.h accordingly.
should go with Rec!2063 (merged) Moore!517 (merged)