Merge pull request #19880 from open-craft/jill/ace-header-block

SE-800 Wraps the email header in a block so it can be themed

openedx/core/djangoapps/ace_common/templates/ace_common/edx_ace/common/base_body.html

@@ -57,6 +57,7 @@
             <td class="header" style="
                 padding: 20px;
             ">
+                {% block header %}
                 <table role="presentation" width="100%" align="left" border="0" cellpadding="0" cellspacing="0">
                     <tr>
                         <td width="70">
@@ -69,6 +70,7 @@
                         </td>
                     </tr>
                 </table>
+                {% endblock %}
             </td>
         </tr>