- apply title_args to accordion title by using setattr

Presumably this could be implemented in kivy.lang, but I wasn't sure what the implications of doing so were. That said, it seems like all arguments passed to kivy.lang.Builder are swallowed, except for the first argument, which is assumed to be a name. 

Rather than passing an argument that will only be swallowed later, I pass the arguments to the instance after it's been built.