Swap special codes 'F' and 'FF'

For consistency with the standard code (and our own documentation on the
Chemistry Updates google doc), we now use 'F' as the flag for HAC
photolysis and 'FF' as the flag for the dicarbonyls simulation. Note that
the same change is required in globchem.dat

Signed-off-by: Jenny Fisher <jennyf@uow.edu.au>