The page template is embedded in the error response

This is a shortcut change since it doesn't make sense to send the error
page template with every error response (the viewer can fetch it from
the server once but that's slightly more work).

static/templates/error.html

@@ -6,6 +6,7 @@
 {{#CSS_URL}}
     <link type="text/css" href="{{{CSS_URL}}}" rel="Stylesheet" />
 {{/CSS_URL}}{{#KIWIX_RESPONSE_DATA}}    <script>
+      const KIWIX_RESPONSE_TEMPLATE = "{{{KIWIX_RESPONSE_TEMPLATE}}}";
       const KIWIX_RESPONSE_DATA = {{{KIWIX_RESPONSE_DATA}}};
     </script>{{/KIWIX_RESPONSE_DATA}}
   </head>