db: phenotypes: Add Probeset data structures...* gn3/db/phenotypes.py (Probeset): New dataclass.
(probeset_mapping): New dict.
* gn3/db/__init__.py: Add probeset_mapping and Probeset.
Add a diffing function...For now the diff function uses the Linux tool "diff" to generate the diff
since it is efficient and straightforward.
* gn3/computations/diff.py (generate_diff): New function.
* tests/unit/computations/test_diff.py: Test cases for ☝🏾.