#105 Ajout de CloisonAval pour prendre en charge les vannes levantes

spec/pab/cloison_aval.spec.ts

spec/pab/pab.spec.ts

spec/structure/structure_vanlev.spec.ts

src/index.ts

src/pab/cloison_aval.ts

src/pab/cloisons.ts

src/pab/pab.ts

src/structure/structure_props.ts

src/structure/structure_vanlev.ts