Add breadcrumbs and UI consistency updates across backoffice templates

templates/backoffice/base.html.twig

@@ -2,3 +2,14 @@
 {% block importmap %}{{ importmap('backoffice') }}{% endblock %}
 {% block title %}Tijd voor de test | {% endblock %}
 {% block nav %}{{ include('backoffice/nav.html.twig') }}{% endblock %}
+
+{% block main %}
+    <div class="container">
+        <div class="mt-3">
+            {% block breadcrumbs %}{% endblock %}
+        </div>
+        {{ include('flashes.html.twig') }}
+        {% block body %}
+        {% endblock body %}
+    </div>
+{% endblock %}