Website: Manual should be more prominent in left sidebar

[Chealer]

It took me a while to find the website's API Separation page today. In hindsight, this is understandable since less important things come higher in the sidebar to the left.

It may be difficult to fully sort the sidebar's elements by importance, but I believe it can easily be improved. Specifically, while facilitating contributions is critical, the manual should surely be above the FOR CONTRIBUTORS section.

[rgoers]

The team has debated this for quite some time. At least one PMC member wants to rewrite the whole manual from scratch. Personally, I think the technology we are using causes the majority of the problems.

[grobmeier]

In the meantime, we could actually move the contributors section down.
I also moved Javadoc, Runtime Deps, Support and Thanks to the "Project Information" section, as I don't think this is relevant except for a few.

[vy]

Fixed by several changes implemented for #2535.

[Chealer]

I (still) think that the manual should be sorted before the Support and Articles and Tutorials pages, but I agree that this is mostly solved.
Thanks @vy