pages (blog_new, common/blog): various blog improvments: - item_id can now be specified in URL parsing, and a filter_keyword is used so future variants can be implemented (e.g. tags) - if item_id is specified, rsm is discarded and only the requested item is retrieved - new template data "items_http_uri" is filled, with links to HTTP versions of items - blog_new is now a simple redirection to common/blog as the later should be generic enough to handle all use cases.