Refactoring

> Originally at https://github.com/kevin-brown/mousetrap/pull/1

This is the pull request that will be used for code review, tracking progress, and eventually generating the patch set for this refactoring.
`Gtk.main_quit` will kill all windows when you may be looking to just close the window the specific window.  Calling `self._window.destroy()` should do the job without closing the other windows.