Add basic ability to download Ordering Batch as Excel spreadsheet

tailbone/templates/ordering/view.mako

@@ -27,6 +27,13 @@
   ${h.stylesheet_link(request.static_url('tailbone:static/css/purchases.css'))}
 </%def>
 
+<%def name="context_menu_items()">
+  ${parent.context_menu_items()}
+  % if request.has_perm('{}.download_excel'.format(permission_prefix)):
+      <li>${h.link_to("Download {} as Excel".format(model_title), url('{}.download_excel'.format(route_prefix), uuid=batch.uuid))}</li>
+  % endif
+</%def>
+
 <%def name="leading_buttons()">
   % if not batch.complete and not batch.executed and request.has_perm('ordering.order_form'):
       <button type="button" id="order-form">Ordering Form</button>