Add support for user defined functions/stored functions (UDFs)

Like InnoDB engine, Columnstore should also support user defined functions.

CREATE TABLE t1(number INT) Engine=Columnstore;
INSERT INTO t1 VALUEs(1),(2),(3),(4),(5),(6);
CREATE FUNCTION square(num INT) RETURNS INT RETURN(num * num);
SELECT number, square(number) FROM t1;
ERROR 1178 (42000): The storage engine for the table doesn't support IDB-1017: Stored function is currently not supported in Columnstore.