in-page TOCtree looks messy

[drammock]

the in-page TOC tree looks quite messy to me:

I've never much liked having the TOCtree as part of the main content, so one solution is to just remove it and let people navigate with the prev/next buttons or the left sidebar links. Another solution is some kind of formatting change: either special-casing these links to have no underline (or a more subtle one?) or possibly adding some visual structure (like bullets or tree-view lines?) to make it seem less chaotic.

Originally posted by @drammock in #1353 (review)