Accept fungal cell types from CL

[cmungall]

Reciprocal: obophenotype/cell-ontology#447

We could keep the cell types in CL, but IMO it's cleaner if CL is pan-metazoan, and FAO becomes analogous to PO, which gross anat and cell types in one integrated ontology for a clade.

If FAO developers agree I can make a PR

[mah11]

I have no objection, as long as it's well documented which cell types live in which ontology.

But it would be good to make sure it's OK with @dianeoinglis too, since I've really only worked with a few yeasts until now.

[dianeoinglis]

I have no objection.