Use Black Code Style instead of pycodestyle.

What is the expected feature or enhancement?
Increased development efficiency, because

• less time is needed to discuss if personal code style preferences do not match
  • pycodestyle leaves room for that
• code style changes are applied or fixed automatically
  • pycodestyle requires developers to fix identified style issues manually

Inspired from Qiskit/qiskit#6361.

Technical Implementation

• install black
• reformat existing code via black folder1 folder 2
• subsequently fail verification if black --check folder1 folder2 returns a non-zero exit code (to force contributors to adhere to the new code style)