SONATA-179 - Add an optional confirmation modal for boolean types

I've added a confirmation modal for boolean types in admin list template.

This modal is optional and is triggered by a "confirmation" parameter, coupled with the "editable" parameter.

In order to add this confirmation modal, code looks like this:

```php
$listMapper->add('enabled', null, array(
    'editable'     => true,
    'confirmation' => true,
));
```

Confirmation modal looks like this:

![capture decran 2013-12-27 a 15 25 00](https://f.cloud.github.com/assets/103900/1814781/b9232d40-6f02-11e3-82d6-538c887a0c54.png)