erp5_web_renderjs_ui: return modification date in precache json dict script response

bt5/erp5_web_renderjs_ui/SkinTemplateItem/portal_skins/erp5_web_renderjs/WebSection_getPrecacheManifest.py

 web_section = context
 
-if REQUEST is not None:
-  modification_date_string = web_section.getModificationDate().rfc822()
-  weak_etag_header = 'W/"%s"' % modification_date_string
-  REQUEST.RESPONSE.setHeader('ETag', weak_etag_header)
-  if_none_match = REQUEST.getHeader('If-None-Match', '')
-  #using 'in' instead of '==' because the header value may contain a suffix
-  #for the server HTTP compression. e.g. "-gzip" suffix for DeflateAlterETag on apache
-  if weak_etag_header[:-1] in if_none_match:
-    REQUEST.RESPONSE.setStatus(304)
-    return ""
-
 # Add all ERP5JS gadget
 url_list = [
   'favicon.ico',
@@ -197,7 +186,11 @@ for precache_manifest_script_id in precache_manifest_url_list:
 
 if REQUEST is not None:
   import json
+  manifest_dict = {
+    'url_dict': dict.fromkeys(url_list),
+    'modification_date': context.getModificationDate().rfc822()
+  }
   REQUEST.RESPONSE.setHeader('Content-Type', 'application/json')
-  return json.dumps(dict.fromkeys(url_list), indent=2)
+  return json.dumps(manifest_dict, indent=2)
 
 return list(set(url_list))