make wiki TOC sidebar collapsible+selfadjustable
problem to solve
On 4:3 screens or small laptop screens, there is not much horizontal space left for the wiki after subtracting both left+right sidebar.
The left sidebar is already collapsible.
So it doesn't make much sense to treat the right sidebar (TOC) differently.
(please consider both proposals! they don't depend on each other and can be both implemented at the same time)
width or fixed
i.e. only use as much horizontal space as needed to avoid horizontal scrollbars, not more (except for a small