Scroll position tracker (scrollspy) + fixes + CSS library (customised)  minified.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)
Merge pull request #5156 from ostezer/mkdocs-activate-scrollspy

Scroll position tracker (scrollspy) + fixes + CSS library minified.