Improve modmod

[hdoordt]

After dogfooding a bit, here's what I think would improve modmod a lot:

• Update already-generated courses
  • Reuse current package.json
  • Reuse slides that have not been generated and are specific to the users context
  • Idea: generate patches that could be applied manually using gix-diff?
• Copy the license
• Generate VSCode settings (e.g. "rust-analyzer.linkedProjects") and recommended extensions
• Allow for easily generating stubs for topics, modules, tracks