use selections in tracking algorithms

Modify tracking algorithms:

• Both PrVeloUT and PrForwardTracking now expect Pr::Selection<LHCb::Event::v2::Track>.
• PrVeloUT no longer takes a container of PVs or applies IP cuts, as these are done in a Pr::Filter instance instead.

Modify v2::LoKi:

• Change namespace { struct _Instantiations { ... }; } in Rec/LoKiTrack_v2/LoKi_v2/LoKiTrack_dct.h as it seems to clash with non-v2::LoKi in some situations.
• Make v2::LoKi functors expect containers of v2::RecVertex.

Modify python configuration:

• Insert Pr::MakeSelection<T> and Pr::Filter<T> before PrVeloUT in RecoUpgradeTracking, configure the filter to apply IP cuts.
• Insert Pr::MakeSelection<T> before PrForwardTracking in RecoUpgradeTracking.

cc: @sstahl