Introduce folders in the tutorials sidebar and sort tutorials

[MakisH]

This is motivated by our sidebar not being scrollable, neither in Firefox, nor in Chromium.
Since we now have way too many tutorials, this is a bit chaotic.

This PR:

• Introduces two folders: Basic cases and Further cases in the sidebar, similarly to our current categorization in the overview page.
• Makes the "Introduction" a folder as well, which now includes two pages: "Overview" and "Visualization", which moves some useful information from the bottom of the previous "Introduction" page. The URL remains the same for the Introduction page (not for the visualization subsection, which should not have too many references yet). This now also looks better and clearer with two pages instead of one.
• Adds a title above the sidebar.
• The title includes a version: This is the version of the preCICE distribution. @uekerman: Should we change this to anything else?

Partially related to #345.

[uekerman]

The folders are good. Also having visualization on a separate page.
I did not look at the rendered website.

[MakisH]

@uekerman I forgot to upload the screenshots, you can now find them in the first post.

[uekerman]

@uekerman I forgot to upload the screenshots, you can now find them in the first post.

Thanks! "Further cases" are prone to run into the same scrolling issue, no?

Would it be a good time to now also sort the cases alphabetically again?

[fsimonis]

Why "Basic" and "Further"?

Normally the antonym of "Basic" is "Advanced".

[MakisH]

Why "Basic" and "Further"?

Normally the antonym of "Basic" is "Advanced".

1. Because that's what we already are using in the overview and I did not want to open that box again now.
2. Because what we mean is essentially "Look at this curated list first" and "If you are looking for something more specific, maybe you will find it here, but they are not necessarily as good". So, "further" is better than "advanced". And not all cases in the "further cases" are advanced.

[fsimonis]

👍 for consistency.

IMO this naming pair has been bad from the start and I agree with you that "Curated tutorials" is a better name for the section of curated tutorials 😉

[MakisH]

Sorted alphabetically and removed the version: