[WIP] Update the community page to use cards

[mit-mit]

Update the community page to look visually a bit more appealing by using cards.

THIS IS WIP, the markdown inside the cards doesn't work property. @parlough said they'd take a look!

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[dart-github-bot]

Visit the preview URL for this PR (updated for commit 8aedc69):

https://dart-dev--pr6900-community-07hzo3dq.web.app

[antfitch]

That looks so much nicer. @parlough, your thoughts?