Add SeedingLayerSetsHits for transient EDProduct of SeedingLayers
Add SeedingLayersEDProducer
Add TrackingRegion::hits(const SeedingLayerSetsHits::SeedingLayer&) interface

The old interface needs to be kept, because some classes use it with
ctfseeding:SeedingLayer's constructed without SeedingLayersESProducer.
I used templates in CosmicTrackingRegion and
RectangularEtaPhiTrackingRegion to avoid copy-pasting.
Migrate LayerHitMapCache to SeedingLayerSetsHits
Migrate HitPairGeneratorFromLayerPair to SeedingLayerSetsHits
Migrate CombinedHitPairGenerator to SeedingLayerSetsHits
Migrate LayerTriplets to SeedingLayerSetsHits
Migrate HitTripletGeneratorFromPairAndLayers classes to SeedingLayerSetsHits
RecoPixelVertexing/PixelLowPtUtilities/interface/PixelTripletLowPtGenerator.h
Migrate CombinedHitTripletGenerator to SeedingLayerSetsHits
Migrate CombinedMultiHitGenerator, MultiHitGeneratorFromPairAndLayers, MultiHitGeneratorFromChi2
Migrate configuration: TobTecLayerPairs_cfi
Migrate configuration: PixelLessLayerPairs_cfi
Migrate configuration: PixelLessLayerPairs4PixelLessTracking_cfi
Migrate configuration: PixelLayerTriplets_cfi
Migrate configuration: PixelLayerPairs_cfi
Migrate configuration: PixelAndStripLayerPairs_cfi
Migrate bunch of configuration files without any knock-on effects
Migrate conversion configuration files
Migrate configuration: thirdStep_cff