Update to styled-components v4

[abotteram]

Summary

This PR can be summarized in the following changelog entry:

• Updated the styled-components package to v4+.

Relevant technical choices:

*

Test instructions

This PR can be tested by following these steps:

• Make sure you have the console open at all times.
• Walk through the examples in the stand-alone app. Make sure no errors or warnings regarding styled components occur.
• Link yoast-components to wordpress-seo and check out snippet-preview-modal-background-color
• In wordpress-seo install all dependencies and build the project.
• Walk through all react components in the plugin.
  • Onboarding wizard
  • Dashboard widget
  • Metabox
  • Sidebar (gutenberg)
  • Search appearance pages

UI changes

• [x] This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Fixes #

[bintzandt]

@Xyfi I get a lot of merge conflicts when trying to move this issue to the https://github.com/Yoast/javascript monorepo.

Could you see if you can fix them? I had a look at them but I lack context from this specific issue.

You can run the following command from the root of the monorepo in order to transfer the branch: ./transfer-branch.sh yoast-components develop update-styled-components-4 This will give some merge conflicts that can be resolved. After resolving them you can push the branch to the repo by executing: git push --set-upstream origin update-styled-components-4

Please ping me when this is resolved and the branch has been created on the monorepo.