New ndep files, update fates, fix some issues

New nitrogen deposition files for future scenarios: SSP245 and SSP370. And now points
to the closest reasonable new CMIP6 SSP ndep file that we have (for clm50, clm45 points
to the old RCP files).

Update FATES to s1.21.0.a7.0.0. Which brings in a list of improvements and bug fixes. New
options include fates-hydro and fates-parteh

Point to all of the available CO2 files, so we can convert them for use by datm.

Bring in new high resolution PFT land-mask SCRIP grid file (MODISv2), as a start to get the -hirespft
option to work in mksrfdata.pl. Mapping files still need to be created.

Add a test that turning on Carbon isotopes does NOT change answers (currently triggered because of #667)