Reorder page from simple to advanced

As a followup on symfony/symfony#10980 I want to propose to reorder the page as the obvious way should come first. I took me way to long to find the correct way :p

I added two headers

- The default ExceptionController
- Override error templates

in order to introduce how override works and moved the controller override to the bottom as that is more advanced.

Author: clemens-tolboom

cookbook/controller/error_pages.rst

@@ -14,21 +14,12 @@ the status code that should be set for the given exception.
 Error pages can be customized in two different ways, depending on how much
 control you need:
 
-1. Customize the error templates of the different error pages (explained below);
+1. Customize the error templates of the different error pages;
 
 2. Replace the default exception controller ``twig.controller.exception:showAction``
-   with your own controller and handle it however you want (see
-   :ref:`exception_controller in the Twig reference <config-twig-exception-controller>`).
-   The default exception controller is registered as a service - the actual
-   class is ``Symfony\Bundle\TwigBundle\Controller\ExceptionController``.
-
-.. tip::
-
-    The customization of exception handling is actually much more powerful
-    than what's written here. An internal event, ``kernel.exception``, is thrown
-    which allows complete control over exception handling. For more
-    information, see :ref:`kernel-kernel.exception`.
 
+The default ExceptionController
+-------------------------------
 The default ``ExceptionController`` will either display an
 *exception* or *error* page, depending on the setting of the ``kernel.debug``
 flag. While *exception* pages give you a lot of helpful
@@ -46,6 +37,9 @@ shown to the end-user.
     pages for arbitrary HTTP status codes even with 
     ``kernel.debug`` set to ``true``.
 
+Override error templates
+------------------------
+
 All of the error templates live inside the TwigBundle. To override the
 templates, simply rely on the standard method for overriding templates that
 live inside a bundle. For more information, see
@@ -129,3 +123,19 @@ Symfony uses the following algorithm to determine which template to use:
     ``exception.json.twig`` for the JSON exception page.
 
 .. _`WebfactoryExceptionsBundle`: https://github.com/webfactory/exceptions-bundle
+
+Replace the default exception controller
+----------------------------------------
+
+Replace the default exception controller ``twig.controller.exception:showAction``
+with your own controller and handle it however you want (see
+:ref:`exception_controller in the Twig reference <config-twig-exception-controller>`).
+The default exception controller is registered as a service - the actual
+class is ``Symfony\Bundle\TwigBundle\Controller\ExceptionController``.
+
+.. tip::
+
+    The customization of exception handling is actually much more powerful
+    than what's written here. An internal event, ``kernel.exception``, is thrown
+    which allows complete control over exception handling. For more
+    information, see :ref:`kernel-kernel.exception`.