Added support to explore citation relations

[timbachmann]

Fixes #6187

Added tab in entry editor to explore citation relations of a specific article. For further information, one can read our project documentation, which is part of this pull request. This project is part of the "Software Engineering" course at Universität Basel, so don't hesitate to comment or suggest changes.

Screenshots:

• [x] Change in CHANGELOG.md described (if applicable)
• [x] Tests created for changes (if applicable)
• [x] Manually tested changed features in running JabRef (always required)
• [x] Screenshots added in PR description (for UI changes)
• [ ] Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[tobiasdiez]

@koppor Wouldn't docs/advanced-reading/citationrelations be a good place for the documentation?

[koppor]

@koppor Wouldn't docs/advanced-reading/citationrelations be a good place for the documentation?

Yeah, @timbachmann Just move the files there (and possibly add the source for the png files)

[koppor]

For auto closing: Fixes #6187

(GitHub does not know Resolved issue for auto closing)

[koppor]

Small note: The commit messages of the new commits are good ones - imperative voice. See https://chris.beams.io/posts/git-commit/#imperative for details

[koppor]

@timbachmann May I ask for the status? I currently don't see where the current working token is located. 😇

[stefan-kolb]

@timbachmann Amazing feature ❤️

[koppor]

Storing references externally

Pro storing "cited by" and "cites" from "external papers" (== not contained in .bib file) into the file

• .bib file is self contained

Con storing in the file

• can be retrieved quite easily on another machine
• bib file pollution

Storing internal references

Internal links within the .bib file:

Pro and con as above

Conclusion

Proposal:

Use a h2 database for storing this information. h2 functionality is already included in JabRef.

NOT chosen:

• Create a file next to the .bib file with .jabref having meta data of the paper
  • Use YAML as format

Future Work (not part of this PR)

Make a "portable" .car file being self-contained. This is a "citation-archive" containing the external link file and the .bib file. This can be imported by another jabref instance.

[koppor]

• [ ] Link to dblp should be put into the documentation https://blog.dblp.org/2019/11/11/open-citation-data-and-dblp/

[koppor]

We all did not find time to finish this PR. Therefore, moving to koppor - to preserve the commits. See https://github.com/koppor/jabref/pull/643