Add a 'serialised' page

[Kilian]

Splitting this off from #392 just to keep singular issues

I would like the ability for Catalog to render on a given URL all the specified pages in one long list.

My use case for this is that I can then use html-sketchapp-cli and point it to this page to render out my components, without needing to duplicate them into a "kitchensink" page like I do now.

For examples, check out the kitchensink page of the style guide from the creator of html-sketchapp-cli: https://seek-oss.github.io/seek-style-guide/sketch-exports/

Reveal.js has a similar setting for pdf export, where if you add the print-pdfquery parameter it shows all pages at once.