Add parameter to chemistry_data to disable Compton Cooling

[mabruzzo]

We should add a parameter to chemistry_data to disable Compton Cooling (this is mostly just a reminder to make sure I do it)

• It would be useful to enable/disable this source of cooling (just like we can do with other sources) to see if this accounts for some remaining discrepancies reported in Grackle delivers inconsistent results when run with and without comoving coordinates #192.
• It would also be useful to be disable this for the sake of supporting custom cooling tables (while this is not officially supported, it is something that has been done in the past).

[brittonsmith]

I'm ok with this. We are accumulating a fair number of parameters to enable/disable various components. We might want to have a think about how to generalize this for grackle 4.0.