adapt interpolator to PrKalmanFitResult

Ya Zhaorequested to merge
interpolator_PrKalmanFitResult into master

Current interpolator only works for TrackFitResult, where FitNode was used. While now the fit result of Kalman Filter uses another class PrKalmanFitResult and another type of node PrFitNode. I adapted current interpolator to PrKalmanFitResult and name it as TrackPrKFInterpolator. It's a useful tool for some ongoing studies like hit efficiency and hit resolution.

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