Simplify spacings

[damianstasik]

Right now we use the wide range of spacings that come from the default Tailwind config, but designs use just a few different spacings. We can simplify it on our end as well and replace (not extend) our spacings and include named spacings, for example:

• px-xs
• px-sm
• px-md
• ...

Edit: Matt added names spacings to designs so it's a super easy migration
Edit 2: Let's clean up the design files to make sure everything uses the tokens.