Add thumb indexes

[tomaz]

Printed book might benefit from using thumb indexes. Each chapter should have one, and for Next chapter each section.

There are 2 challenges:

1. Get thumb indexes working in LaTeX
2. Make sure edge-to-edge printing will work on lulu (it should be supported, but may require couple trial runs to be sure...)

As for LaTeX solution itself, I imagined either a separate TOC would get inserted (I think before main one), on odd page (right side on two page spread).

I played with it in the past, but didn't find working solution. I tried first with thumb-index package (don't remember which one), but it wasn't compatible with existing packages. So tried solution based on tikz which did work on the TOC page, but didn't pursue to make it visible on all pages; ran into some issues and abandoned it.

An idea from this issue