Upgrade styled-components to v5

Release notes here: https://github.com/styled-components/styled-components/releases/tag/v5.0.0

More info here: https://medium.com/styled-components/announcing-styled-components-v5-beast-mode-389747abd987

And migration notes (should just work): https://styled-components.com/docs/faqs#what-do-i-need-to-do-to-migrate-to-v5

The TLDR is: A lot faster and with support for hooks. Yay! 🎉