DEPS: Add easy-unit sources

Summary

Adds the sources of easy-unit to the repo

Focus

• The 0.0.1 version of easy-unit has been releases by it's maintainers and so we can use that one from now on.
• The server-repo should have three easy-unit jar-files now:
  1. The compiled classes
  2. The javadoc
  3. And the sources (new!)

Test Environment

Please extract the sources jar-file and confirm, that the sources are in there

Check List for the Author

• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there spezifications? Are they satisfied?