Interface private subroutines use HCO_GC_ prefix

[lizziel]

The HEMCO interface in hemco_interface.F90 contains private IRF subroutines that use prefix HCO_GC_. However, this can cause confusion with the HEMCO interface within GEOS-Chem which uses the same prefix convection. I believe the _GC_ in the HEMCO interface for CAM is short for gridded component. _GC_ in GEOS-Chem means GEOS-Chem. I suggest we rename these subroutines in the CAM interface to avoid confusion with GEOS-Chem.

[lizziel]

There is a similar naming issue for the public HCOI_ subroutines in hemco_interface.F90. The naming would indicate they are defined in HEMCO but they are actually defined in HEMCO_CESM.

I suggest we replace HCO_GC as well as the HCOI_ prefixes in hemco_interface.F90 with hco_cesm_. This would conform to the standard for other models that use HEMCO, including the HEMCO standalone. The second entry indicates where the subroutine is defined. hco_sa is standalone and is in HEMCO. hco_gc_ is in GEOS-Chem. hco_cesm_ would be in CESM. Core hco_ and hcoi_ subroutines, e.g. hco_run, would be reserved for HEMCO proper.