Fix #265 limit nodeType property to sections

src/app/examples/pab-complete-chain.json

src/app/formulaire/definition/concrete/form-courbe-remous.ts

...pp/formulaire/definition/concrete/form-regime-uniforme.ts

...formulaire/definition/concrete/form-section-parametree.ts

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

src/app/formulaire/fieldset.ts

src/app/formulaire/formulaire-element.ts