suzerain: avoid feeding negative mass fractions to chemistry sources

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44376 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: plot all the data + colors

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44377 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: permit downsampling

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44378 0bd85f0b-c151-43b9-a1e9-27231104551f