(bug 25072) Fix weirdness in collapse threads

The problem was the use of find(), which is fully recursive, instead of
children() (now using the children ">" selector with find as per Krinkle
comments), which only search for the inmediate children. Since this
function is called recursively for .lqt-thread-replies this prevents
adding nested replies twice.

Also, modified the toggleCollapse function adding
'.lqt-post-wrapper, .lqt-thread-replies' to children() so it only
hides and shows messages and thread replies, leaving other elements that
aren't displayed anyway. This is to prevent it from also hiding the title
of the entire thread, which also contains the action links: that was
increasing the weirdness on pages with several threads.

Change-Id: I520b0451d55f4eae2bbcf795c46f975b4b0af63b
Merge "(bug 25072) Fix weirdness in collapse threads"