Add and improve semantic structure of home page

[yshng]

• Add <header>, <footer>, and <main> tags to the corresponding components.
• Add <h1> to "Polis" at the top of the page.
• Change remaining headers to <h2>
• Change header tag used for emphasis to <strong> to signal importance.

Addresses both #60 and #61.

[yshng]

@thomassth @NewJerseyStyle Any insight into why this is failing the check?

[thomassth]

Possibly the cypress was listening for element types instead of content

[yshng]

@thomassth Does this mean there isn't actually a problem and the PR can be approved? (barring any other issues with the code)

[thomassth]

The cypress test files should get some touchup I think o

[NewJerseyStyle]

Thanks @yshng 💖 I think it is fine, they are known issues. We will correct this misbehavior of E2E test on Thursday with @cplkake if he is available. We can wait for that patch first and then merge this by weekend.

[NewJerseyStyle]

Funny thing is, all tests passed on our local machine, so I'd merge this first and think about is later