More confirmed species in a few models.

Only CH2* remains in USC-Mech, and there's not (yet) a way to represent that.
Tidy up the comments added to the output thermo file.
Allow "singlet[CH2]" and "triplet[CH2]" in known species SMILES file.

There's no way to write these to the file via the web interface,
but you can manually edit the file before you start the import job.
I have added to a few models.
Other species that have no SMILES representation could be added to this
special-case dictionary.