tagbbs: rewrite index

support thread
index rebuilding
no more global tag (all posts)
bbs name changed to title of post:0
webui: simple thread view
webui: hide links when not logged in
webui: concise routing
tagbbs: disable post:00000 like posts
webui: fix a put error on non yaml doc
sqlstore: return rev match instead of error
webui: set timeout
webui: minor tweaks
webui: showdown plugin for @ and #
webui: fix put on empty list
webui: fix @ in links