Functions, aggregates, and user types

Querying system.schema_* tables directly to get information about user-defined functions, aggregates, and user types.

Currently, the system tables are the only method of displaying information about user-defined functions, aggregates, and user types.

Procedure

Show all user-defined functions in the system.schema_functions table.
```
cqlsh> SELECT * FROM system.schema_functions;
```
Show all user-defined aggregates in the system.schema_aggregates table.
```
cqlsh> SELECT * FROM system.schema_aggregates;
```
Show all user-defined types in the system.schema_usertypes table.
```
cqlsh> SELECT * FROM system.schema_usertypes;
```