Reasoner-validator

- "error.knowledge_graph.edge.attribute.value.empty" should NOT be triggered by numeric zeros either!

- Puzzling issue with validation of some qualifier values turned out to be a bug in the Biolink Model 3.5.2, resolved in 3.5.3, so fixed unit tests accordingly. This release doesn't have any core functional changes to the code but users of earlier versions should be aware that validation with Biolink Model releases earlier than 3.5.3 may give puzzling qualifier value validation messages.

- 'False' attribute values now properly handled; all other 'empty' values trigger an error message

- Add additional JSON element path context to "critical.trapi.validation" validation messages
- Remove TRAPI Response JSON sanitization, since TRAPI 1.4.2 is now the 'latest' and desired validation standard

- Non-destructive TRAPIResponseValidator.check_compliance_of_trapi_response(response) validation of TRAPI Response JSON (release 3.8.3 bug removed Message)

- Fixed TRAPI release management to cache TRAPI GitHub code release and branch tags locally - in a **versions.yaml** file - to avoid Git API calling denial of service issues; Small **scripts/trapi_release.py** utility script provided to update the **versions.yaml** file, as periodically necessary.
- YAML file management tech debt cleaned up a tiny bit. Tweaked a couple of validation codes for this reason.
- Added DEVELOPER_NOTES.md to guide uniform project release management (especially, of the esoteric bits of the project like TRAPI release and validation code updates)