Add 'full table of contents' page to docs

Add a "full table of contents" page to the docs at /contents.html (lists all sections, with no depth limit). We're no longer using the front page as a table of contents (instead it's a welcome page with a written overview of the structure of the docs). It's useful to have this full toc page that lists everything but it's long and not pretty so put it on its own page.

This may have broken latex waiting to test on rtd