add tools.partial for setting selected input params to fixed values;
improve 'masking' behavior in model_plotter for > 3D models


git-svn-id: svn+ssh://svn.mystic.cacr.caltech.edu/mystic/mystic@743 968178ea-60bd-409e-af13-df8a517b6005
Merge branch 'master' of https://github.com/uqfoundation/mystic