Draft: status-page: Limit vertical size

We want the scrolled windows of the list boxes to propagate their natural height but we don't want a status page to grow larger than the quick settings (for now) as that would push down the notification area permanently. So in order to avoid that allow to limit the status pages size based on another widget (in this case the quick settings flow box).

While at that I've fixed some minor nits and eliminated a stack in a stack as that just triggers more complex widget allocations.

This can go away once @arun-mani-j 's improved flow box lands as we then show/hide the status page dynamically not allocating any vertical height when not shown.