feature symfony#23680 [Webprofiler] Added blocks that allows extension of the profiler page. (Nyholm)

This PR was squashed before being merged into the 3.4 branch (closes symfony#23680).

Discussion
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[Webprofiler] Added blocks that allows extension of the profiler page.

| Q             | A
| ------------- | ---
| Branch?       | 3.4 (to be retargeted)
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Im not sure if we allow this but I thought I would try to submit this PR.
The [TranslationBundle](https://github.com/php-translation/symfony-bundle) is extending the Symfony profiler page for translation. It would be great if it didn't have to replace all the contents but just replace some smaller blocks.

Commits
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ffd25fb [Webprofiler] Added blocks that allows extension of the profiler page.

Author: fabpot

src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/translation.html.twig

@@ -82,6 +82,8 @@
 
     <h2>Translation Messages</h2>
 
+    {% block messages %}
+
     {# sort translation messages in groups #}
     {% set messages_defined, messages_missing, messages_fallback = [], [], [] %}
     {% for message in collector.messages %}
@@ -108,7 +110,9 @@
                         <p>None of the used translation messages are defined for the given locale.</p>
                     </div>
                 {% else %}
-                    {{ helper.render_table(messages_defined) }}
+                    {% block defined_messages %}
+                        {{ helper.render_table(messages_defined) }}
+                    {% endblock %}
                 {% endif %}
             </div>
         </div>
@@ -127,7 +131,9 @@
                         <p>No fallback translation messages were used.</p>
                     </div>
                 {% else %}
-                    {{ helper.render_table(messages_fallback) }}
+                    {% block fallback_messages %}
+                        {{ helper.render_table(messages_fallback) }}
+                    {% endblock %}
                 {% endif %}
             </div>
         </div>
@@ -147,11 +153,16 @@
                         <p>There are no messages of this category.</p>
                     </div>
                 {% else %}
-                    {{ helper.render_table(messages_missing) }}
+                    {% block missing_messages %}
+                        {{ helper.render_table(messages_missing) }}
+                    {% endblock %}
                 {% endif %}
             </div>
         </div>
     </div>
+
+    {% endblock messages %}
+
 {% endblock %}
 
 {% macro render_table(messages) %}