Backend 'UniteEns': utilise uniquement modèles. + code modernization.

app/formations/edit_ue.py

app/formations/formation_io.py

app/models/formsemestre.py

app/models/ues.py

app/scodoc/sco_bulletins_json.py

app/scodoc/sco_bulletins_xml.py

app/scodoc/sco_formsemestre_exterieurs.py

app/scodoc/sco_ue_external.py

tests/unit/sco_fake_gen.py

tests/unit/test_formations.py