Save all opened files.

        Iterate through self.data and call save() on any modified files.

def save_all(self):
        """Save all opened files.

        Iterate through self.data and call save() on any modified files.
        """
        for index in range(self.get_stack_count()):
            if self.data[index].editor.document().isModified():
                self.save(index)