Support for Virtual field for Doctrine

[dxmaster]

This changes make is possible to make 'virtual" field for Doctrine ORM. This code use code described here https://github.com/floriansemm/SolrBundle/issues/171 for new documents, and my code for update documents. Added new attibute for annotation field: trackedFields. This attribute contains list of fields. If one of this fields is updated, then will updated Virtual fields in Solr

Example: `/**

• @Solr\Field(getter="getHasVideo", trackedFields="trailer,youtubeGameplay")
• @var boolean */ private $hasVideo;

/**

• Get hasVideo
• @return boolean */ public function getHasVideo() { if (($this->trailer !== null && $this->trailer != "") || (count($this->youtubeGameplay) > 0)) { return true; } else { return false; } } `