Prompts user to input a date in the past.

def pastdate(self, prompt, default=None):
        """Prompts user to input a date in the past."""
        prompt = prompt if prompt is not None else "Enter a past date"
        if default is not None:
            prompt += " [" + default.strftime('%d %m %Y') + "]"
        prompt += ': '
        return self.input(curry(filter_pastdate, default=default), prompt)