Add List component

[sarahmonster]

Closes #50.

Draft of docs here: https://www.notion.so/octopusthink/List-1645bf94c66740ce805382c99be83de4

I've made it so it just borrows a bunch of props from the Paragraph component, since it would make sense to style these similarly. It does mean we're basically repeating a whole bunch of code, so we may end up wanting to have some sort of base Text component for components like these at some point (Quote comes to mind, for instance, although that might use slightly different styling, so maybe not?) but for now some repetition is probably fine.

Here's what else I think we need here:

• Review + add docs (@tofumatt )
• Add an optional Heading prop
• Add a prop to swap between bulleted and numbered lists
• Implement an icon list variant (reliant on Icon component #14 and probably best done as an enhancement ticket)
• Figure out the best way to handle the individual list items (@tofumatt)

I've tagged you in the items I'm not sure how to handle, but I may need help with the other ones too—I'm going to see how far I get now.

For the last item especially, I'm not sure how to do this exactly.
I do like the format in the README, so maybe we can work backwards from there and see if we can build the API to make it super easy to make a list? Also, I'm betting this could be weird with Markdown processing, so I'm super out of my depth here.

[sarahmonster]

For reference, the accessibility docs I relied on pretty heavily here; there may be more to borrow from in the future.

• http://kb.daisy.org/publishing/docs/html/lists.html
• https://fae.disability.illinois.edu/rulesets/LIST_1/

[sarahmonster]

Okay, I think we are FINALLY good to go here, if you want to give the code a once-over? I think technically it's my PR so you need to review it, even though you probably wrote more code here.

[tofumatt]

🚢 once the linting errors are fixed. You can check them in Azure or with npm run lint locally.