Draft: Multi-user shared state system

[sr258]

Hi to all developers using h5p-nodejs-library,

I've been working on a multi-user shared state system that allows interactive live activities similar to the one already available on h5p.com. It's still in an experimental stage but there's a first draft. I'd love to hear you thoughts on this!

General introduction (with demo and links to code): https://wp.srettig.de/a-proposal-for-an-open-source-multiuser-extension-for-h5p/

Technical specification: https://github.com/Lumieducation/H5P-Nodejs-library/blob/master/packages/h5p-shared-state-server/README.md