Migrate TrackVertexUtils from Rec to LHCb

The code in TrackVertexUtils is really just an extension of the LHCb::State interface, so to sort out a circular dependency in Rec (Phys/SelTools -> Phys/SelKernel, Phys/SelKernel -> FunctorCore, Phys/FunctorCore -> Phys/SelKernel,Phys/SelTools) the easiest solution (for this part) is to move this code (which is needed by Phys/SelKernel, and some code there has to be moved to a 'lower' point, but that implies that this code first has to move to a sufficiently 'low' point) into the same package as LHCb::State, which is Event/TrackEvent. It could even move into State.h and State.cpp eventually...

must be applied in conjunction with Rec!2801 (merged)