Move sub-navigation to the head of the page

[StephanEwen]

The new Java has put the sub navigation on top of the page. I think that other pages should also consider that.

[fhueske]

👍 Maybe it can be integrated such that text can flow around it?

[StephanEwen]

We can also think about a different layout, where the subnavigation is at
the side, and the documentation topics is on the top (like a second menu
bar or so). Just a thought.

I also would very much like if someone else than Ufuk would take charge of
the website. Ufuk has loads of things to do right now...