Created method called after fetch

`preLoad`: It is useful to filter data by complex conditions in relatively simple query and then use it it data loading (main) query.
`postLoad`: 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
{
    private $ids = array();

    protected function doCreateQuery(Queryable $repository)
    {
        // process query which loads only @...ToOne relations
    }

    public function preFetch(Queryable $repository, $limit = NULL, $offset = NULL)
    {
        // process filtering of main entity IDs
        $this->ids = $ids;
    }

    public function postFetch(Queryable $repository, \Iterator $iterator)
    {
        $result = iterator_to_array($iterator, TRUE);
        // process loading of all needed relations in @...ToMany direction
    }
}
```
Updated to `postFetch` to be compatible with Doctrine naming. It is also shorter :-)