Revitalize zuehlke.github.io

_This PR is part of the 1316_ZUEHLKE_GITHUB_2021 Z-Task and is intended to be merged during the deployment session on Wednesday, December 16th._

Re-implement the application from scratch in React
Partially adapt the design to the current corporate page
Ensure all external links (corporate page, social media) are up-to-date
Implement a mechanism which automatically updates the Contributions and People data using the GitHub API
- Replaces the current manual selection process deciding which repos and users are shown on the page
Add a GitHub Actions workflow which automatically builds and deploys the application on every push to the develop branch

Zuehlke / zuehlke.github.io