OTP Token add failed because of invalid function call. qr_widget doesn't contain `on_value_changed` method since it inherits from `IPA.widget` and not from `IPA.input_widget`. Emitting the event was preserved for future possible usage. https://fedorahosted.org/freeipa/ticket/4306 Reviewed-By: Adam Misnyovszki <amisnyov@redhat.com>