Adding support for reading stylistic set names out of the font.

I believe I added this in a way that looks like it fits with what was already there: just after it takes other names out of the name table, and I'm using the same self._skimNameIDs() method.

There will be another related pull request in defconAppKit/controls/openTypeControls.py to add these stylistic set names into the control that FeaturePreview makes use of.