web.page-catalog: structurally and visually handle sub-pages #88
Description
A sub-page is defined as a page that appears within others (images, audio files, etc), and thus are primarily recorded by players through indirect navigation. In the case of sub-pages that appear exclusively inside a single one (e.g. level front images) those can be grouped in a similar fashion as the folder -> pages nesting in the explorer.
Open to debate: whether such pages should amount to the total counters (as any non hidden ones).