Added shortcut methods for controllers

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#11593)
| Applies to    | 2.6+
| Fixed tickets | 

This commit is associated to https://github.com/symfony/symfony/pull/11593 that adds new shortcut methods to controllers.

If anything is wrong with my commit or this description, please tell me and I will fix it as soon as possible. I'm glad I finally try to help this awesome project.

Same thing here - we should replace all the old code with the new `addFlash` method