Better support for reduced-permissions users

With only the settings 'administer site information' and 'administer site appearance' but not 'administer site configuration', path 'admin' says 'You do not have any administrative items.' To get to the theme list, you have to click 'By Module' then 'Configure' under 'System' which doesn't make much sense.

I believe the main problem is that the top-level menu items have permission requirements that are too strong, which prevents users from navigating to the things they are allowed to do, and that giving those users the permissions needed for navigation also gives them undesired power. However, there appears to be other things going on behind the scenes as well, possibly including the connection with the new toolbar.