bug #5431 Updated the code to display flash messages (aykin, javiereguiluz)

This PR was submitted for the 2.6 branch but it was merged into the 2.3 branch instead (closes #5431).

Discussion
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Updated the code to display flash messages

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | -

Commits
-------

c2676ae Improved the code used to display flash notices
176cdc6 Update the_controller.rst

Author: wouterj

quick_tour/the_controller.rst

@@ -330,9 +330,11 @@ And you can display the flash message in the template like this:
 
 .. code-block:: html+jinja
 
-    <div>
-        {{ app.session.flashbag.get('notice') }}
-    </div>
+    {% for flashMessage in app.session.flashbag.get('notice') %}
+        <div class="flash-notice">
+            {{ flashMessage }}
+        </div>
+    {% endfor %}
 
 Final Thoughts
 --------------