support post tags, auto generate TOC by tag

[zeronetscript]

these commits implements blog tag function. with this: 1.every post can have multi tags , which appears in details part , 2.every tag (or untagged) appears as a link , which links to a TOC page of this tag(or show all untagged). 3.an overview TOC page, show all tag: n post(s), helps user navigate to that tag TOC (same as 2)

these changes consider upgrade from old data condition, user can overwrite index/js/css/dbschema then get all these functions