server (blog): implemented tag/category filtering: - the tag=[quoted tag] query is used to use the filtering - MAM data use request.mam_extra instead of request.extra_dict to avoid using it with item_ids - getDefaultQueryData function is used to keep query data (link MAM category filtering) between links - filtering is help when displaying a blog post, this way it's easy to navigate between thematic posts - filtering can be removed by clicking on user avatar/nick (with default theme)