`ALTER TABLE` support

`ALTER TABLE` is commonly used in import SQL scripts. Adding foreign keys after loading data into tables appears to be one of the more common uses in import scripts.

**Examples:**
* [Chinook_PostgreSql_utf8.sql](https://github.com/morenoh149/postgresDBSamples/blob/master/chinook-1.4/Chinook_PostgreSql_utf8.sql) uses `ALTER TABLE` to add foreign key constraints to created tables after data has been loaded.
* [dellstore2-normal-1.0.sql](https://github.com/morenoh149/postgresDBSamples/blob/master/dellstore2-normal-1.0/dellstore2-normal-1.0.sql) uses `ALTER TABLE` to add primary key constraints as well as foreign key constraints after data has been loaded.

 
**Use cases:**
- [x] Add primary key
- [x] Add foreign key constraint
- [ ] Alter owner