Refactor overview page

[bethcollins92]

Homepage (/certified)

• Change “Ubuntu Certified hardware” to “Ubuntu certified hardware” (capitalisation)
• Add a “Laptops” section to the homepage as the first section
• Probably requires design, as now there are 5 sections rather than 4. I wonder if these should become full-width sections now?
• Remove the “Models” drop-down (is this word used anywhere else? Let’s try to kill it)
• Simplify section titles - e.g. “Ubuntu Desktop certified hardware” should be simply “Ubuntu certified desktops”