Replace mutable propagator members by always checking the direction from the seed
Set trajectory builder in the constuctor of ConversionTrackFinder
Deliver TkCloner to TransientInitialStateEstimator

Requested by @VinInn to ease resolution of future merge conflicts.
Move construction of four helpers from beginRun() to constructor in ConversionTrackCandidateProducer
Remove ParameterSet member from ConversionTrackCandidateProducer