v1.5 massive (code) update

• Massive code update
  • Finally add flake8 config
  • Use pre-commit (and pre-commit hook) to ensure future better coding style
  • Reformat a lot of modules with black => Coding style
• Reuse username as mail address if it looks like a mail address
  • Add it to the user profile
  • Add it as unconfirmed mail address and trigger confirmation mail