Moved the 'Administrator role' setting to a new 'Role settings' form at admin/people/role-settings

A new "Role settings" form is now available at admin/people/role-settings as another tab under "People" (next to "Roles" and "Permissions"), which requires the 'administer permissions' permission to be able to access.

This is the new location for the "Administrator role" setting that used to appear at admin/config/people/accounts on the "Account settings" form. The setting has direct control over site permissions, so a user now needs permission to administer permissions to change it.