Added a new mode to temporal statistics for in situ use.

Added the ability to incrementally update temporal statistics while timesteps come through a data source such as in situ. In this situation, it is not possible for the filter to stream time from its input as only one timestep is available at a time. Instead the filter works with the current timestep accumulating statistics as the filter is executed. The filter always outputs the statistics of all the so far processed timesteps in this mode.