Optimize object permission queries by using django-guardian's prefetch util

Advances AlekSIS-Core#407 (closed), blocked by AlekSIS-Core!540 (merged)

aleksis/apps/alsijil/templates/alsijil/class_register/week_view.html

@@ -333,11 +333,13 @@
                   </a>
                 {% endif %}
               </h5>
-              <p>
-                {% for assignment in person.person.group_roles.all %}
-                  {% include "alsijil/group_role/chip.html" with role=assignment.role small=assignment.date_range %}
-                {% endfor %}
-              </p>
+              {% if group_roles %}
+                <p>
+                  {% for assignment in person.person.group_roles.all %}
+                    {% include "alsijil/group_role/chip.html" with role=assignment.role small=assignment.date_range %}
+                  {% endfor %}
+                </p>
+              {% endif %}
               <p class="card-text">
                 {% trans "Absent" %}: {{ person.person.absences_count }}
                 ({{ person.person.unexcused_count }} {% trans "unexcused" %})