Prepare remote data

[floesche]

• Previously, running pixi run subset-medium showed some warnings. These are fixed now.
• The data used in search (and external services like neuDiff) contained a lot of unused data and was only available as js. Now, the data is also available as json, which speeds up processing.
• some logic errors for the caching of (empty) files were resolved.

[leburnett]

A few commands in the guides that should be removed / updated but otherwise, pixi run subset-medium generated the pages without errors.

[floesche]

I added more fixes of the documentation to #142

[leburnett]

Thanks for adding these changes. Was there anything else that needed updating? Otherwise, it looks good to me now.