Reorganize Select classes, update Verificateur GUI

DEVELOPERS.md

e2e/check-translations.e2e-spec.ts

src/app/calculators/solveur/config.json

src/app/calculators/verificateur/config.json

...mponents/select-field-line/select-field-line.component.ts

src/app/formulaire/definition/form-solveur.ts

src/app/formulaire/definition/form-verificateur.ts

src/app/formulaire/elements/fieldset.ts

src/app/formulaire/elements/select-field-custom.ts

src/app/formulaire/elements/select-field-nub.ts

src/app/formulaire/elements/select-field-parameter.ts

src/app/formulaire/elements/select-field.ts

src/locale/messages.en.json

src/locale/messages.fr.json