Meganav prototype v2 b (flat products)

[sowasred2012]

Done

• Added v2 of the mega nav prototype, the first of two variants (the first is here)
  • This one features a "flat" layout on the products dropdown

Not to be merged - for demo purposes only

QA

• Check out this feature branch
• Run the site using the command ./run serve or dotrun
• View the site locally in your web browser at: http://0.0.0.0:8001/

Issue / Card

Fixes https://github.com/canonical-web-and-design/web-squad/issues/4835

[webteam-app]

Demo starting at https://ubuntu-com-11292.demos.haus