This allows loading spinners, modals and other components with a real
fullscreen background to stretch over the required space, without being
covered by the navigator or other sibling components.
This also requires the collapsed navigator to have a 1px margin-right,
or its separation border won't be visible.
The performance of the page is heavily degraded by components loaded
dynamically via defineAsyncComponent that recursively carry behind the
whole Vue machinery.
By wrapping defineAsyncComponent calls in shallowRef we make sure that
we only wire the root level of the newly created dynamic component.