API: diverses corrections, tests unitaires (sauf absences et logos).

app/api/absences.py

app/api/departements.py

app/api/etudiants.py

app/api/formations.py

app/api/formsemestres.py

app/models/etudiants.py

app/pe/pe_jurype.py

app/pe/pe_tools.py

sco_version.py

tests/api/README.md

tests/api/test_api_departements.py

tests/api/test_api_etudiants.py

tests/api/test_api_evaluations.py

tests/api/test_api_formations.py

tests/api/test_api_formsemestre.py

tests/api/test_api_logos.py

tests/api/test_api_partitions.py

tests/api/test_api_permissions.py

tests/api/tools_test_api.py

tools/fakedatabase/create_test_api_database.py