Prepare the book website

In progress

[ ] once the book is out and has an URL/DOI etc., we should of course add that too

[x] replace the sidebar color, replace "The OSCAR project" in the navbar with the book title #5
[x] create a top index page which has an enumerated list of all chapters, listing their titles and authors. The titles are hyperlinks to subpages (e.g chapter_05.md so you don't have to think about fancy file name). #7
[x] in each subpage add a title and again the author names, and dump in the code #7
[x] then the book chapter authors can have their way and improve their pages. But they don't have to worry about what to put where etc., we already provide a framework
[x] bonus points for setting up some javascript or so to add a little "copy to clipboard" link to each code block. #17