Tidy up /pages directory

[fnwbr]

As of Next.js 13 they have also changed the recommended way of structuring an app directory structure: https://nextjs.org/blog/next-13#new-app-directory-beta - and in the following minor releases they have further adjusted it: https://nextjs.org/blog/next-13-1#improved-reliability-and-support-for-app-directory (via)

We should probably follow that restructuring...

Also, when running next build with our current setup, it's falsely assuming that some of our files are pages. When they're just components we're wanting to use inside of other pages. For example /etherpad/actions/AddExistingPad is a component we use inside of /etherpad/[[...roomId]].

The solution for the latter problem is to probably make use of this: https://nextjs.org/docs/pages/api-reference/next-config-js/pageExtensions#including-non-page-files-in-the-pages-directory (via)