Reuse the same controller that was used for adding children,
`WorkPackageChildrenRelationsController`, and renamed it to
`WorkPackageHierarchyRelationsController`. The difference is done with a
`relation_type` parameter which can be `"parent"` or `"child"`.
Reuse the same dialog that was used for adding children,
`AddWorkPackageChildDialogComponent`, and renamed it to
`AddWorkPackageHierarchyDialogComponent`.
Christophe Bliard