Submit Button Class Counts

[TrevorBurgoyne]

add optional arg to submit button that will add a field to the callback arguments that contains info about the number of non-deprecated annotations in each class. currently users have to duplicate the counting logic internal to ulabel, when really it could be provided via some api. Speaking of which there should also be a ULabel get_class_counts() method or smth to get the counts that are displayed in the toolbox class counter item.