Unify constituent minimum values across schemes

[peverwhee]

When run-time constituents are registered in a scheme with an instantiate call, a minimum value is supplied. If the same constituent is registered by multiple schemes and that minimum value differs, the model will error.

Among possibly other options, we could:

1. Create a lookup method that is accessible by any scheme that would enable you to get the "proper" minimum value and set it.
2. Initialize every constituent with min value = 0 and then have a scheme that calls set_minimum for each registered constituent.

related to #332

issue noted by @jimmielin in #327

[jimmielin]

I added this file https://github.com/ESCOMP/atmospheric_physics/blob/6c3f3fa4dcdb4fbd687e2d8fe30170e04164b147/to_be_ccppized/ccpp_chem_utils.F90

to replicate the existing qmin value logic specified in CAM's src/chemistry/mozart/chemistry.F90::chem_register

I am thinking of potentially modding CAM to use this as well so we don't duplicate the values.