Fixes for race conditions between Realtime plugin and the AJAX display of inline...

Fixes for race conditions between Realtime plugin and the AJAX display of inline replies.

* keep the notice-reply-placeholder around, but hidden
* insert things before the placeholder, rather than appending to the end of the list.
* append the active form after the hidden placeholder, so things inserted before the placeholder never come after it
* Realtime: check pre-existing notice visibility a second time after loading the HTML for a notice. Fixes bug where sometimes your own post would be shown twice because the Realtime notification arrived before the AJAX posting returned, but Realtime's AJAX fetch of the notice returned after.