concrete implementation of AbstractObjectManagerInitializer for Doctrine\ODM\Mongo\DocumentManager

concrete implementation of AbstractObjectManagerInitializer for Doctrine\ODM\Mongo\DocumentManager

Require PR : https://github.com/doctrine/DoctrineModule/issues/168

Sample configuration : 

    return array(
        'service_manager' => array(
            'initializers' => array(
                'documentmanager_initializer' => 'DoctrineMongoODMModule\Initializer\DocumentManagerInitializer'
            ),
        ),
    );