suzerain: #3107 add ignore_gramp_{mean,rms} flags

Intent is to use these to permit effectively zeroing
growth rates during simulations.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44939 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: #3107 warn on unimpl. flag

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44940 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: #3107 implement ignore_gramp_{mean,rms}

Implement these two ignore flags.  In the process, reorders
some of the initialization logic slightly to avoid looking
up baseflow information until it is actually needed.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44941 0bd85f0b-c151-43b9-a1e9-27231104551f