Fix TypeScript compilation error and is-replying-mark bug.
Post, save and render multireplies

Some problems remain: float drop with 2d layout, closed threads placed
before multireplies.
Insert multireplies at correct location when loading one at a time.
Highlight/zoom-to multireplied post when hovering/clicking multireply

And fix #/post-123 bud (should be #post-123 with no '/').