Use the "sia_" prefix in the ConstantInColumn class.

Also: IceFlowLawFactory makes sure that "prefix" is not empty.
Use "std::vector<double> &" instead of "double *" in function arguments.
Implement "-atmosphere one_station".

This atmosphere model reads scalar time-series of the near surface air
temperature and precipitation and uses them at all grid points in the
domain. Resulting climate fields are constant in time *unless* a
modifier such as lapse_rate is used to create spatial variability.

Use "-atmosphere_one_station_file" to specify the name of the file
containing "air_temp" and "precipitation" variables.