Suggestion: Moving content of `slides` folders to tutorials

[bebatut]

Hi,

For a while, I found the slides folders in topics confusing:

• The content is a bit lonely on its side
• It can not be listed as prerequisite or follow-up in tutorials (in different topics)

What we can do:

• moving content of the slides folders to tutorials
• use the subtopics and define one as "introduction" that always goes to top

What do you think about this?