Fixed bug in drawing order of atoms in some functional groups.
Fixed bug in drawing order of atoms in some functional groups.

When I added exceptions for O2, HO2, etc. I needed the heavy atom to be
printed last. However, I inadvertently caused all non-carbon functional
groups to have their heavy atoms printed last, e.g. ethanol would appear
as CH3-CH2-HO instead of the correct CH3-CH2-OH. This commit corrects the
bug by only making the heavy atom last for the special cases.

KEHANG/RMG-Py,KEHANG/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,pierrelb/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,chatelak/RMG-Py,nyee/RMG-Py,enochd/RMG-Py,enochd/RMG-Py,nyee/RMG-Py