Deprecate add/remove_class.

From the widget roadmap: https://trello.com/b/5Xaj8Z7j/widgets
The idea is to make add/remove class discouraged, but not unavailable.  I was worried those who used to use it may wtf (what the "fudge", politely) when they get a deprecation warning.

Are you suggesting I
A) Not mention _add/remove_class at all.
B) Change the language from `please use` to something more discouraging.
?