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)

@sstahl @decianm @ahennequ