Change LogError to cms::Exception in SeedingLayerSetsBuilder::updateEventSetup

This is anyway rather catastrophic failure from mismatch between
SeedingLayer configuration and conditions.
Add theTTRHBuilders member to SeedingLayerSetsBuilder

To allow obtaining hits directly from HitExtractor, bypassing
SeedingLayer (to be committed later).
Remove hasPredefinedHitErrors from SeedingLayer(SetsBuilder)

It is not used anywhere, and it makes the code simpler to remove it.
Deliver TTRHBuilder to HitExtractor instead of SeedingLayer itself

Only the TTRHBuilder was used from SeedingLayer anyway.
Add SeedingLayersEDProducer-friendly interface to SeedingLayerSetsBuilder
Migrate SeedingLayerSetsHits and SeedingLayersEDProducer to the new interface of SeedingLayerSetsBuilder
Rewrite SeedingLayerSetsBuilder::hits()
Deliver hits to SeedingLayerSetsHits with swap-style interface