Show announcements in timetable views

Blocked by AlekSIS!184 (merged)

Closes #63 (closed)

aleksis/apps/chronos/templates/chronos/partials/hints/substitutions.html

-{% load martortags %}
-{% if hints %}
-    <ul class="collapsible">
-        <li>
-            <div class="collapsible-header " style="font-size: 16px;">
-                <div class="col s12">
-                    <i class="material-icons left">announcement</i>Es gibt {{ hints|length }}
-                    Hinweis{{ hints|pluralize:"e" }} für diesen Tag.
-                    <i class="material-icons right collapsible-trigger"></i>
-                </div>
-            </div>
-            <div class="collapsible-body">
-                {% for hint in hints %}
-                    <div>
-                        <strong>
-                            {{ hint.classes_formatted }}{% if hint.teachers and hint.classes.all %},{% endif %}
-                        </strong>
-                        {% if hint.teachers %}
-                            <span class="badge new green no-float no-margin">Lehrkräfte</span>
-                        {% endif %}:
-                        {{ hint.text|safe_markdown }}
-                    </div>
-                {% endfor %}
-            </div>
-        </li>
-    </ul>
-{% endif %}