Clean up duplicate directory trees demo/lang and Languages

[PieterOlivier]

courses/Recipes/demo/lang and courses/Recipes/Languages contain a very similar directory tree. The content of the files differs in some places though.
This results in confusing very similar trees on the website:
https://www.rascal-mpl.org/docs/Recipes/Languages/
vs
https://www.rascal-mpl.org/docs/Recipes/demo/lang/

We should really clean this up.

[jurgenvinju]

Additionally:

• demo projects should show the full code of their functions and other definitions. In MissGrant there is already no sign of this.
• The demo's are also missing opportunities for using screenshots.

How are we going to integrate the to narratives: recipes and the actual demo code? One solution would be to not include the demo integrally near the recipes anymore, only as part of the standard library and other libraries like Rascal-lsp. The recipes could ((include)) selected material from the source code of the demo modules.