fix backlinks, don't redraw convos on each post

Fixes the double backlinking bug I accidentally introduced.
Speeds up page loading.  Also various minor fixes.
~~Third commit makes it so quoting a post always change to that conversation (previously it only happened if you weren't in a conversation already, and the new conversation wasn't "General").~~
Revised: Quoting a post always changes to that conversation unless you have something in the convo field not in the current list.  The presumption is that you typed it in yourself and want to change the conversation topic.