schema: add user.flag_is_system_admin to db. user.class: add property flag_is_system_admin. unit tests: add test for user.flag_is_system_admin. top nav (head.php): loop through eq_groups; if user is manager of any eq_group, then show 'manage groups/users' link in nav, and add admin link for system admins. top nav (index.php): remove content, keep simple welcome message and add instructions for sign in. footer: create modal with help info and link. head: remove admin list of eq_groups (obsolete)