Merged local-refactor-koleary
Simplify layout structure, switch to keyed 'layout' actions, remove most options, force either blocks or regions to be placed within a region
Switch to children (instead of subregions) in the layouts definition; initial stab at fractional sizing and add a blocks/region toggle
Reset footer region to be a unconfigurable region like the other to avoid confusion
Rename PageVariant to DisplayVariant; adjust file path, annotation and routes
Added missing variable region_id in theme hook, adapted template
Removed region.id() from layout region template