Hide or collapse sidebar if empty

Problem/Motivation

When the sidebar is empty, it should be hidden or at least collapsed.

This may for example happen if visiting
/user/login
where no other page is avaialble yet, having access denied on all pages logged out.

Then the empty sidebar looks confusing.

Furthermore, when hiding the sidebar in the login area manually via the burger menu icon and reloading the page, it's currently reappearing.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes