Completely re-reading the controller chapter

| Q   | A
| --- | ---
| Doc fix? | yes
| New docs? | no
| Applies to | 2.3+
| Fixed ticket | n/a

Hi guys!

This follows #4427, but only for the controller chapter (I will open separate PR's for `from_flat_php_to_symfony2`, `routing`, and `templating`).

This is more than just updating for the best practices. This is about face-lifting these important chapters after several years of us as a community realizing what's more important and what's less important. More notes:

- I removed some information about using the `defaults` to pass additional information to your controller from this chapter. This is too early and we have this now: http://symfony.com/doc/current/cookbook/routing/extra_information.html

- I removed `ContainerAware` information. This is not the right spot... and maybe nothing is. I don't see much use-case for this - it seems like you'd either extend the base Controller or register your controller as a service.

- I kind of want to remove or move the forwarding stuff. I can't find a real use-case for doing a forward from one controller to another. It adds a lot of overhead and I don't see any situation for it.

Thanks!
even if you didn't extend the base class, you could still use it as controllers that do extend the base class. See the examples in the beginning of this article as an example. I think this should be reworded. (as you are better in that than me, I'll leave the exact words up to you)