feature #4433 Completely re-reading the controller chapter (weaverryan)

This PR was merged into the 2.3 branch.

Discussion
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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!

Commits
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903f52c Fixing build error
ceb7b94 Big update based on feedback from xabbuh and WouterJ
6ef10db Moving forwarding section all the way to the bottom
0754efc Completely re-reading the controller chapter

Author: weaverryan