Appends the given value(s) to the attribute (column).

def append_data(self, attribute, values):
        """Appends the given value(s) to the attribute (column)."""
        found = False
        if type(values) != list:
            values = [values]
        for col in self.Table:
            if attribute in col:
                dict_values = [u"{0}".format(value) for value in values]
                col[attribute] += dict_values
                found = True
        if not found:
            raise KeyError(attribute)