Site improvements

[encukou]

Notes from the sprint:

• [ ] Review breadcrumbs. Ideally they should correspond to the URL structure, but specific exceptions are fine. Test this.
• [ ] Review <title> tags. They should start with something specific.
• [ ] Review the URL structure. Deleting stuff after any / should take me to a reasonable page.
  • [x] Do year-based pagination for runs
• [ ] Redesign homepage – use big buttons: "chodím na kurz" / "jsem samouk"
  • [ ] Remove the links from the site-wide navbar
• [ ] Redesign the list of self-taught courses
• [ ] Add links to individual "other topics" to the list of self-taught courses
• [ ] Add arrows to non-course lesson pages bases on canonical courses they appear in
• [ ] Add possibility to hide solutions
• [ ] Remove execution counts from Notebook renders
• [ ] Add session-specific times and places
• [ ] Add session numbers to titles, breadcrumbs, session pages
• [ ] Session page: don't show header if there are no materials
• [ ] Add “Add to calendar” button to calendar pages
• [ ] Add lesson summaries
  • [ ] Aggregate summaries on session backpages
  • [ ] Add link to backpages to material lists (if there are any summaries)
• [ ] Skip session backpage in ←/→ navigation if there's nothing there
• [ ] A Session's → link should go to the first lesson, if there is one
• [ ] Add infoboxes to session pages