Minor Release with basic Trivadis CI enhancements

Added

• add markdownlint configuration file .markdownlint.json
• add syntax highlight theme trivadis.theme
• add new Trivadis logos 2021
• add Trivadis title image

Changed

• adapt pipeline with a new job for the markdownlint.
• Add information about .markdownlint.json to
  AUTHOR_GUIDE
• adjust link color to Trivadis default
• adjust footer to new CI
• adjust title to new CI

Removed

• old Trivadis logos removed