CSRF refactoring : done !

I've changed some thing in this refactoring but without no BC break (except one manipulation for all).

- Batch actions are now a real select box and UI is now "Javascript enhanced".

- Batch actions are CSRF protected.

- If object_action is not CSRF protected, it is rendered as a simple link

- If object_action is CSRF protected, it is rendered as a simple link

- If object_action is CSRF protected and Javascript is available, action is automatically posted

- If object_action is CSRF protected but Javascript unavailable, you have to handle an intermediate page (I will doc this point). Delete action is using this principle. If Javascript is not available, you'll now be redirected on an intermediate page. Here is the BC Break: **you have to** create in your admin generated resources/views the MyModelDelete/index.html.twig with following code:

```twig
{% extends_admingenerated "MyBundle:MyModelDelete:index.html.twig" %}
```

this file will be required only if Javascript is not available.

This is just for existing projects. This file will be auto-generated using the command.

For CSRF protected actions (batch_actions, object_actions), request is made in POST. Does actions (in list view) need to be CSRF protected?


I'll create another PR for documentation.