Change mechanism of evoking smoothing in KalmanFitter to that when propagation reaches endOfWorld

Current KalmanFitter only performs smoothing if all trackStates have been filtered. As long as the propagation misses a measurement surface (e.g. an outlier), the smoothing won't be triggered. A temporary way out is to trigger smoothing when the propagation reaches the endOfWorld. This could lead to overdoing of the propagation, thus a better way should be figured out in the future.