Call stopListening on module stop

When answering [the question on stack overflow about event unbinding](http://stackoverflow.com/questions/22410200/marionette-js-questions-about-events-and-how-to-correctly-unbind-them/22435769) I've noticed that we don't unbind events when calling stop on module.

The documentation said that:

> A module can be stopped, or shut down, to clear memory and resources when the module is no longer needed.

But actually it doesn't and it can be reason for some memory leaks.

So I propose to call `stopListening` on module in `stop` method.