New algorithm to decorate Acts track particles with truth links.

The original TrackFindingValidationAlg, which already computes truth
matching probability etc.,  is split into a base now used by the
TrackFindingValidationAlg and the new TrackParticleTruthDecorationAlg.
The latter decorates track particles with links to truth particles and
the associated matching probability, hit efficiency and hit purity.

Moreover the base algorithm is modified in such a way that the
statistics gathering is compile time optional. Although, it is
currently enabled for both algorithms.