Let DebateHtml.layoutPage start on new param rootPostId
Let DebateHtml.layoutPage start on new param rootPostId

- Compare the post id with the root post, instead of the PageBodyId (and
  update Post.meta accordingly).
- Since post '1' hereafter will not always be the root post of the
  rendered page, use .dw-depth-0 insetad of #dw-t-1 or #dw-post-1, in
  CSS and Javascript.
- Remove unused Javascript that mention #dw-post-1 and #dw-t-1

debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old,debiki/debiki-server-old