Allow register button to be replaced

templates/forms/register.html.twig

@@ -44,7 +44,9 @@
     </div>
 
     <div>
+        {% block register_submit %}
         <button type="submit" class="btn btn-block btn-primary">{{translate('REGISTER_ME')}}</button>
+        {% endblock %}
     </div>
     
     <div style="padding-top: 10px;">