Adds a group over all the given tables (will include any rows between the first row over all
        tables, and the last row over all tables)
        Initially collapsed if collapsed is True (True by default)

def add_row_group(self, tables, collapsed=True):
        """
        Adds a group over all the given tables (will include any rows between the first row over all
        tables, and the last row over all tables)
        Initially collapsed if collapsed is True (True by default)
        """
        self.__groups.append((tables, collapsed))