Move SeedingLayerSetsHits to TrackingTools/TransientTrackingRecHit

In order to avoid a package with only one class. SeedingLayerSetsHits
can be thought as a very specialized container of
TransientTrackingRecHits.
Merge pull request #2527 from makortel/moveSeedingLayerSetsHits

Reco cleanup -- Move SeedingLayerSetsHits to TrackingTools/TransientTrackingRecHit package