Updated sidebar to expand to show clicked subtopics, and no sliding.

Here's what I came up with so far, @66eli77, @jtamiace, @rtibbles.
I think moving to the system you suggested of having the system only respond to the URL, and make clicks affect the URL only would be the best way to do this. Then we could make the highlighting happen during the navigation events. We also already have the paths on the topic_nodes, so they could just be links.