Finish landings

[sapegin]

• Fix headings
  • h1 should wrap whole book name, now it's “From apprentice to master”
  • Maybe remove h2 with the book name, it repeats the main heading and creates weird document outline
  • Adjust all other heading levels to make sure we don't use the same level for content that supposed to be nested
  • Split book description Mardown files into two — move headings to React (Non-unique IDs on the homepage #102)
  • h2 shouldn't look bigger than h3 on the main page
• Fix book covers
  • Move book covers to React (Do not wrap aligned images in paragraphs in Markdown #110)
  • Use SVG images
  • Add bottom margin after covers on small screens
• Use the new Tip component instead of “black hole”
• Inline buy buttons
• Add hr styles
• Make a component for testimonials
  • Make column widths equal
  • Fix layout on smallish screens
  • Make the container the same with as page content
  • Align columns with page content columns
• Make a component for heading (frontpage, front-header-wrapper, etc.)