Store the column family key validator in system tables. Please note that we derive the validator from CQL partition keys and never actually read it from the database. This is different from Origin which uses CompositeType that is both stored and read from the system tables. Fixes #7. Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com> Tested-by: Pekka Enberg <penberg@cloudius-systems.com>