Refactor to styled-components

[emplums]

Refactors all of our components to use styled-components and removes our system-component custom setup 🙌

Notes:

• I'm removing the OcticonButton component because it's essentially a <Link><Octicon/><Link>

To Do

• Add is to all propTypes objects that use it
• Add theme to all propTypes
• Double check default theme doesn't ever override custom theme (especially when spreading theme out of proto component)
• Add test that makes sure default theme is applied to every component
• Make sure every component has a test for system props
• . Create a codemod
• add babel plugin [wait to do this after removing Primer CSS]
• fix PointerBox

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[shawnbot]

This is EPIC, @emplums. Nice work! 👏

[shawnbot]

I'm sure you're aware that there are a ton of console errors in the test suite. Let me know if I can help you work through some of those.

[mxstbr]

Gave the diff a quick read, this looks amazing! 👏👏👏 Good job! 💯

[mxstbr]

Should this be PropTypes.node instead of PropTypes.func? As far as I can tell the way the is prop is implemented should mean any element or component can be passed, not just function components.

[emplums]

Good catch!

[emplums]

Going to merge this into the release branch and do a separate docs PR!

[mxstbr]

🎉🎉🎉🎉🎉🎉🎉🎉🎉🎉