This hides the top-bar by default for everything besides paint/sculpt workspaces. - Use the top-bar mainly for active tool settings & popovers panel options. (transform / snap settings are an exception for this convention). - Only show the top-bar (by default) in paint work-spaces (sculpt / texture-paint / grease-pencil). - Add an active-tool panel to the sidebar. - Split 3D view tabs into (Item / Tool / View). D4721 with minor changes. Further work is needed for the top-bar and image-editor.