MkDocs Theme: Sticky nav-bars and better scaffolding.

This PR introduces:

 - Auto-scrolling main navigation menu (disabled by default on mobile)
 - Auto-scrolling TOC pane (disabled by default on mobile)
 - Redesigned TOC pane
 - Better-ised scaffolding that is more native bootstrap than custom hacks.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)