added the ability to run raw query

This feature allow you to execute rawQuery directly from the library [elasticsearch-php](https://github.com/elasticsearch/elasticsearch-php). 

Sometimes we need to do some complex queries and would be nice that we could run it for an easy way.

For example
````php
$manager = $this->get("es.manager");
$repository = $manager->getRepository('AcmeDemoBundle:City');

$latitude = 40.00;
$longitude = -2.5;
$distance = 12;
$me = 'someId';

$query = array(
    "size" => $limit,
    "sort" => array(
        array(
            "_geo_distance" => array(
                "location" => array(
                    "lat" => $latitude,
                    "lon" => $longitude
                ),
                "order" => "asc",
                "unit" => "km"
            )
        )
    ),
    'query' => array(
        'filtered' => array(
            'query' => array(
                'match_all' => array()
            ),
            'filter' => array(
                'and' => array(
                    'filters' => array(
                        array(
                            'geo_distance' => array(
                                'distance' => $distance . 'km',
                                'location' => array(
                                    'lat' => $latitude,
                                    'lon' => $longitude
                                )
                            )
                        ),
                        array(
                            'not' => array(
                                'filter' => array(
                                    'term' => array(
                                        '_id' => $me
                                    )
                                )
                            )
                        )
                    )
                )
            )
        )
    )
);

$nearbyCities = $repository->search($query);

````

You can also run the query as a string json
````php
$manager = $this->get("es.manager");
$repository = $manager->getRepository('AcmeDemoBundle:City');

$query =  '{
    "query": {
        "term" : {
            "slug" : "some-slug"
        }        
    }
}'

$someCity = $repository->search($query);
````