Create new atm process to read in gas concentrations

Radiation expects profiles for
```
active_gases = (/ &
'H2O', 'CO2', 'O3 ', 'N2O', &
'CO ', 'CH4', 'O2 ', 'N2 ' ).
```
co2, ch4, n2o are namelist variables assumed to be spatially invariant in EAM. Prescribed O3 should be read in. H2O profiles should come from qv as used by the rest of the model. I'm not sure where CO should come from.

We should create a new atm process (which is really just a stub for future chemistry work) which uses ScorpioInput to read in and create these prescribed fields. I don't think this is needed for v0 since it already accomplishes this... somehow. Just a C++ exercise.