Achem uses a different solar code than the rest of the model

[mathomp4]

In looking at Achem because of GEOS-ESM/GOCART#140, I noticed that Achem has its own solar zenith angle code that is not consistent with the rest of GEOS, which uses MAPL_SunGetInsolation. I know recently @dr0cloud enabled fancier orbital parameters, etc for the GEOS sun code, and the question is: should Achem use that same code so they use the same sun?

Now, perhaps Achem needs to use a different zenith angle code because the files it's trying to apply a diurnal cycle to used a different code? I'm not sure. But in the future, perhaps the files being read will have been generated by code using the MAPL sun code and this might need to be changed.

For now, I'm going to "assign" to the chemistry folks I sort of think of with Achem, but I might not know the right ones. Please re-assign to the right people.