Update HTML for custom edit modal buttons

apps/openassessment/templates/openassessmentblock/oa_edit.html

 {% load i18n %}
 
-<div id="openassessment-edit">
-    <script id="metadata-editor-tpl" type="text/template"><!-- empty --></script>
+<div id="openassessment-edit" class="editor-with-buttons">
     <textarea class="openassessment-editor"></textarea>
-    <input type="button" class="openassessment-save-button" value="{% trans "Save" %}"/>
-    <input type="button" class="openassessment-cancel-button" value="{% trans "Cancel" %}"/>
+    <div class="modal-actions">
+        <h3 class="sr">Actions</h3>
+        <ul>
+            <li class="action-item">
+                <a href="#" class="button action-primary openassessment-save-button">{% trans "Save" %}</a>
+            </li>
+
+            <li class="action-item">
+                <a href="#" class="button openassessment-cancel-button">{% trans "Cancel" %}</a>
+            </li>
+        </ul>
+    </div>
 </div>