Hotfix-001 -> v0.1.1-alpha

This an emergency fix. In the main branch, it seems to be the case, that two legacy folders slipped in:

• .github
• notebooks

These shall not be there, and more importantly not on GitHub. This MR deletes those folders, and marks it as a hotfix.

This means, this will go directly to main (and GitHub respectively) and it will get the first patch version (v0.1.1-alpha). The hotfix branch shall be not deleted, but merged into dev afterwards.