Add JDBC feature DatabaseMetaData.getColumns

This PR implements DatabaseMetaData.getColumns
```
ResultSet getColumns(String catalog,
                   String schemaPattern,
                   String tableNamePattern,
                   String columnNamePattern)
                     throws SQLException
```


More info here :
http://docs.oracle.com/javase/7/docs/api/java/sql/DatabaseMetaData.html#getColumns%28java.lang.String,%20java.lang.String,%20java.lang.String,%20java.lang.String%29