Resolve "Substitutions: Empty teacher drop-down"

Closes #173 (closed)

aleksis/apps/chronos/templates/chronos/edit_substitution.html

 {# -*- engine:django -*- #}
 
 {% extends "core/base.html" %}
-{% load material_form i18n %}
+{% load material_form i18n any_js %}
+
+{% block extra_head %}
+    {{ edit_substitution_form.media.css }}
+    {% include_css "select2-materialize" %}
+{% endblock %}
 
 {% block browser_title %}{% blocktrans %}Edit substitution.{% endblocktrans %}{% endblock %}
 {% block page_title %}{% blocktrans %}Edit substitution{% endblocktrans %}{% endblock %}
@@ -21,4 +26,6 @@
       </a>
     {% endif %}
   </form>
+  {% include_js "select2-materialize" %}
+  {{ edit_substitution_form.media.js }}
 {% endblock %}