feat: add Learn path, change menu icons to use the new design

[scorebreaker]

Add Learn path, change menu icons to use the new design. Also, I decided to use inline svg-s for the menu icons, because otherwise I would have needed to use hacky ways to get the hover working (https://css-tricks.com/the-many-ways-to-change-an-svg-fill-on-hover-and-when-to-use-them/).

[stackingcats]

Thank you. Looks good in general.
A few concerns:

• Would it be worth the effort to dynamically fetch the videos instead of hard-coding them?
• When navigating to the learn view, I get an error
  Failed to execute ‘postMessage’ on ‘DOMWindow’: The target origin provided (‘https://www.youtube.com’) does not match the recipient window’s origin (‘https://localhost:3000’).
  and lots of warnings
  Some cookies are misusing the recommended “SameSite“ attribute
  Please let's wipe those off.

[stackingcats]

Maybe would make sense to group all the menu icons under one story?

[scorebreaker]

Done.

[scorebreaker]

• Would it be worth the effort to dynamically fetch the videos instead of hard-coding them?

Done.

• When navigating to the learn view, I get an error
  Failed to execute ‘postMessage’ on ‘DOMWindow’: The target origin provided (‘https://www.youtube.com’) does not match the recipient window’s origin (‘https://localhost:3000’).
  and lots of warnings
  Some cookies are misusing the recommended “SameSite“ attribute
  Please let's wipe those off.

I couldn't find solution to Failed to execute ‘postMessage’ on ‘DOMWindow’ issue, I checked that it is related with youtube iframe get call (tjallingt/react-youtube#96), but not caused by react-youtube library. Also, "Some cookies are misusing the recommended “SameSite“ attribute" is still an issue as well - from what I researched, cookies are controlled from server-side and youtube should take care of cookies itself.