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!
Hm, if you are reading the book for the first time, you will probably never have heard anything about the service container when you are reading this chapter. So, is it really good user experience when you have to skip a section in the book or don't understand it at all?