W-based rho

A rho based on W is directly supported at the time of this writing. The file mpisppy.utils.find_rho.py can compute rho using a cost input file that is created by the gradient software. If you want to use W values as the cost, you would need to modify the code in wxbarwriter.py to write the final W values in the right format (i.e., that matches the cost output format used by the gradient software).