Empty state papercuts

A few minor issues with the current empty state:

• When the leaflet is unfolded both sides look very similar, which looks weird. I'd drop the stuff on the right side and have the view just be emtpy
• There's a grayed-out secondary menu. I'd hide it instead.
• I think we have a more compact style class for sidebar statuspages (at least in libadwaita, not sure about libhandy), I'd use that styling here as the placeholder in the sidebar is a bit too large visually
• The search button is grayed out, I'd also hide that instead when it's not available