Smyle usermods

[nanr]

Description of changes

Adding SMYLE specific changes to CESM2.1.4 release

Specific notes

Setting SMYLE-specific changes

Contributors other than yourself, if any:
Erik Kluzek, Jim Edwards

CTSM Issues Fixed (include github issue #):
Fixes #1197

Are answers expected to change (and if so in what way)? No

Any User Interface Changes (namelist or namelist defaults changes)? User-mods directory added, but I'm not sure it's used.

Testing performed, if any:
(List what testing you did to show your changes worked as expected)
(This can be manual testing or running of the different test suites)
(Documentation on system testing is here: https://github.com/ESCOMP/ctsm/wiki/System-Testing-Guide)
(aux_clm on cheyenne for intel/gnu and izumi for intel/gnu/nag/pgi is the standard for tags on master)

NOTE: Be sure to check your coding style against the standard
(https://github.com/ESCOMP/ctsm/wiki/CTSM-coding-guidelines) and review
the list of common problems to watch out for
(https://github.com/ESCOMP/CTSM/wiki/List-of-common-problems).

[ekluzek]

@nanr let's schedule a time to talk about this say tomorrow? One comment we had is that the namelist_definition_datm.xml file in the source mod directory should be smaller or handled in a different manner than it is currently in order to cut down on repeated code and make it more maintainable. But, I also need to know a bit about when these changes need to come in and how they need to be coordinated with other CESM tags.

[ekluzek]

@nanr we should chat about this one a bit. Is this important for the SMYLE work that is happening? Do you need this to happen soon? thanks

[ekluzek]

@jedwards4b can you help me figure out the relationship between this PR and #1614 which you created? From what I can tell your PR supersedes this one as it converts the user-mod directories into a use-case. But, I'm not sure that the new PR covers all the options available here (1850, HIST to present day, and CPLHIST mode). The new PR also doesn't include changes to DATM that are needed for each of these for offline.

[ekluzek]

I met with @nanr and @jedwards4b to talk about this. We think this one just needs to be closed. SMYLE simulations are mostly done now. What's left to do are coupled simulation as per the #1614 PR.

#1614 also takes care of #1197 by using a use-case rather than user-mod directories.