Duplication problem in user_mods

Right now we have duplication of user_mods for NEON for use with big leaf CLM and FATES. Because of the way we need to include various commands and parameters for all NEON sites and others for specific NEON sites, when we added user_mods to run CTSM-FATES we just duplicated all the folders. This means that if we update any site in the big-leaf set of folders, we also have to update it in the FATES set of folders, and vice versa.

We should come up with a way to remove this duplication without it being too convoluted and difficult for a naive user/developer to understand.