Created method called after fetch

It is useful to load some extra relations which could negatively affect performance if it would be included in main query.

It can be used in following way
```php
class ComplexQuery extends QueryObject
{
    protected function doCreateQuery(Queryable $repository)
    {
        // process query which loads only @...ToOne relations
    }

    public function doAfterFetch(Queryable $repository, \Iterator $iterator)
    {
        $result = iterator_to_array($iterator, TRUE);
        // process loading of all needed relations in @...ToMany direction
    }
}
```
I think that `onAfterFetch()` would be better