rose edit: tweak latent page display

At the moment, a page is always displayed regardless of
`View Latent Pages` status if it has no relevant sections
or if it has sub-pages. This functionality guards against
having pages such as the `namelist` page appear as a
latent page (greyed out) and similarly for the parent page
for a group of duplicate sections.

However, this leads to a lot of irrelevant, undesirable pages
appearing by default in some configurations. For example,
every duplicate section will appear as a non-latent page (
see the example in the demo_meta suite below).

The best logic is to say that all pages that are parents of
non-latent pages must be displayed as non-latent. Every
other page with no content can then be described as latent
and hidden correctly.
Can `8` be a constant of the class?