Task: In the context menu of "All entries", there needs to be a new entry "Add JabRef suggested groups"

It should add following groups (if not already existing!) at the end of the groups:

• "Entries without linked files"
• "Entries without groups"

Tasks:

• Implement logic functionality
• Add tests for logic functionality (can be done iteratively with task 1 to ensure test-driven development)
  • No group existing: both groups should be added
  • One group already existing: only other group should be added
  • ... and more ...
• Implement UI functionality (add context menu entry and call functionality)
• Disable UI context menu if the two groups already exist

The groups show as follows in JabRef: