Content files restructure for compatibility with Hugo

[fsimonis]

The hugo migration will become significantly less hacky if we bring the current content into a hierarchical format that reflects the page structure.
Moving them around in jekyll should not be an issue, as we use permalinks in all pages.

To use the navigation features, we should use the navigation hierarchy as the content structure with folders:

• quickstart
• docs
• tutorials
• community
• about

IIRC some things cannot be directly mapped to the hierarchical structure, such as https://precice.org/docs.html which should be docs/index.html but really is docs/fundamentals/index.html.

Furthermore, some sections in the docs don't have an overview page.

Finally, it is still unclear to me how to handle the nested sections such as https://precice.org/configuration-mapping.html which should be docs/configuration/basics/mapping. Such subsections may need some overview pages too.

[fsimonis]

The structure we should aim for is shown here: https://gohugo.io/content-management/organization/#organization-of-content-source

[MakisH]

Are you only talking about moving around files, or also changing the structure of the rendered content?

[fsimonis]

For preparing the migration I am talking about changing the file layout of the sources only.

The consistent use of permalinks should result in identical rendering of the page.

[fsimonis]

I did an initial restructuring in #580.

There are still some todos:

• the filenames need to be cleaned up as they will be the page names in the output. Prefixes need to be removed.
• sections need _index.X files. These can be empty or contain the full overview, but they need to exist for hugo to recognise folders as sections.