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
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 configuration: MixedLayerPairs_cfi
Migrate bunch of configuration files without any knock-on effects
Migrate conversion configuration files
Migrate configuration: thirdStep_cff
Migrate configuration: secondStep_cff