Changes to support climatologies for temporal statistics with temporal parallelism.

Climate scientists often want temporal statistics to support
climatologies (e.g. averages over seasons instead of the entire
time span). This is the first step in doing that while also
using temporal parallelism.
Statistics for spatio-temporal parallelism seems to be working for gregorian calendar.
Making vtkMultiBlockTemporalStatistics work in serial.

We want to make sure the filter is available in serial so that
users can set up the spatio-temporal pipeline in a serial build
and/or run of ParaView.
Cleaning up the GUI and serial usage.

Making it work for a single process run when ParaView was built with MPI
as well as for when we have no time steps.
Some more fixes and adding in a test for the spatio-temporal statistics.
Merge pull request #6 from aashish24/temporal_parallelism_statistics

Temporal parallelism statistics