Currently, page_sidebar() and page_navbar() take an explicit sidebar argument.

However, for page_auto(), which is used in Express mode, there's no sidebar argument (because children can't be passed as named arguments in Express). Instead, we inspect the *args, pull out any Sidebar objects, and then explicitly pass them to the sidebar argument.

Also, because of how Python handles named and unnamed ages:

• For page_sidebar(), the signature is page_sidebar(sidebar, *args). This means that the sidebar must be the first argument and must not be named.
• For page_navbar(), the signature is page_navbar(*args, sidebar). This means that the sidebar must not be the first argument, and must be named.

I think we should remove the sidebar parameter from these functions and simply inspect the *args for Sidebar objects -- essentially, take the logic from page_auto() and move it into page_sidebar() and page_navbar().