[READY] BELONGS_TO through

How to use:

```
public function relations()
{
	return array(
		'category' => array(self::BELONGS_TO, 'ArticleCategory', 'category_id'),
		'club' => array(self::BELONGS_TO, 'Club', array('club_id' => 'id'), 'through' => 'category'),
	);
}
```