add tests for after/until/before/since keywords

Summary

tests for caosdb-server!12 (merged) (Issue caosdb-server#132 (closed))

Focus

• One further test in test_query.py
• removed nose functions on the go

Test Environment

Nothing special. pipeline should be sufficient.

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?

For further good practices have a look at our review guidelines.