loads a contract file

        :param filepath: (string) - contract filename
        :return: source, err

def load(filepath):
        '''
        loads a contract file

        :param filepath: (string) - contract filename
        :return: source, err
        '''

        try:
            with open(filepath, "r") as fh:
                source = fh.read()
        except Exception as e:
            return None, e
        return source, None