Revert "Do not use save-button from core."

This reverts commit fd04f2fb.

aleksis/apps/untis/templates/untis/untis_import.html

@@ -37,9 +37,7 @@
   <form method="post" enctype="multipart/form-data">
     {% csrf_token %}
     {% form form=upload_form %}{% endform %}
-    <button type="submit" class="btn waves-effect waves-light green">
-     <i class="material-icons left">cloud_upload</i> {% trans "Import" %}
-    </button>
+    {% include "core/save_button.html" %}
   </form>
 
 {% endblock %}