NodeAdminController: Make list overridable

I suggest to change all private members to protected. Had a use case where I needed to override the Node Admin List, therefore I had to make a child bundle and override the Controller (and admin list configuration). While the members are private this cannot be done "easily"
do only one query to render node tree in link chooser popup
Merge pull request #117 from Kunstmaan/link_chooser_performance

do only one query to render node tree in link chooser popup
Return any response given from Entity

This change enables a developer to issue any kind of response to the slug controller.
In my case I need to be able to have normal CMS functionality and a Form in the page. To be able to handle the submission I needed to be able to forward the request to a certain controller.
This can be done by returning a forward response to the slug controller, like so:

```
/**
     * @param ContainerInterface $container The Container
     * @param Request            $request   The Request
     * @param RenderContext      $context   The Render context
     *
     * @return void|RedirectResponse
     */
    public function service(ContainerInterface $container, Request $request, RenderContext $context)
    {
        $path['_controller'] = 'AcmeDemoBundle:Default:test';
        $path['context'] = $context;
        $subRequest = $container->get('request')->duplicate(array(), null, $path);

        return $container->get('http_kernel')->handle($subRequest, HttpKernelInterface::SUB_REQUEST);
    }
```
Merge remote-tracking branch 'origin/patch-2'