Show a finer-grained table of contents in sidebar

[doyougnu]

According to the sphinx docs we should be able to do something like:

html_sidebars = { '**':
                  ['localtoc.html',
                   'relations.html',
                   'searchbox.html'
                   ]
                }

in conf.py, unfortunately for whatever reason this makes the landing page for the book (and every page actually) a blank white screen on chrome and firefox 🤷

This ticket is done when:

• We have a fine grained table of contents in the sidebar
• It actually works without nuking all content in the book.

I suspect this is a css issue because the page source still contains the content of each .rst file. I bet the sidebar is expanding to the whole screen or something strange like that.