Seeding layers for70 x

According to what agreed on 14/03/05 at the ORP, this PR backports to 70X the following 71X PR's:
#2378 Seeding Layers ESProducers to EDProducers and HLT config related changes
#2527 (fix of the above: move SeedingLayerSetsHits)
#2571 (bug fix in the PixelTrackProducer)