custom handler: retrieve servers from ERP5 storage

data/computer_overview.json

@@ -2,6 +2,7 @@
   "portal_type_source": "Computer",
   "portal_type_title": "computer",
   "portal_type_fields": "computer_fieldlist",
+  "portal_type_mapper": "subscriptions",
   "initial_query": {"include_docs": true, "limit":[0,8]},
   "form": true,
   "view": "web_view",