Changed: small refactoring of the default ViewController for easier reus...

...e

By using the Template Method Pattern, extending the default
ViewController gets easier.

Example usage (untested):
```php
<?php
/**
 * File containing the ViewController class.
 */

namespace Acme\Controller\Content;

use eZ\Publish\Core\MVC\Symfony\Controller\Content\ViewController as BaseViewController;

class ViewController extends BaseViewController
{
    protected function renderLocation( $location, $viewType, $layout = false, array $params = array() )
    {
        if ( $location->id == 42 )
        {
            return $this->render(
                "Acme:full:article_42.html.twig",
                array(
                    "location" => $location,
                    "additionalData" => generateSomeAdditionalData(),
                ) + $params
            );
        }

        return parent::renderLocation( $location, $viewType, $layout, $params );
    }
}
```