Added shortcut methods for controllers

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (symfony/symfony#11593)
| Applies to    | 2.6+
| Fixed tickets | #4666 

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.

We need a versionadded:: 2.6 block above this:

```rst
.. versionadded:: 2.6
    The ``redirectToRoute()`` method was added in Symfony 2.6. Previously (and still now), you
    could use ``redirect()`` and ``generateUrl()`` together for this (see the example below).
```