user anno - new category names must validate against schema

[bkmartinjr]

See categorical.js::categoryNameError() - the user entered category name is validated for uniqueness against the category names in the categoricalSelection summary object. This object is only guaranteed to have a subset of annotation category names in the schema, so it not detect all collisions. Collisions can occur with continuous annotations, the index, or other categorical annotations not displayed for some other reason (see controlsHelpers.js::selectableCategoryNames() for other logic).

We need to test for name uniqueness in the obs annotation schema, not in the display categories.