If a node extends from another node (e.g. ChallengeQuestionNode, NoteNode, AnnotatorNode) also fetch i18n files of its parents (MultipleChoiceNode, OpenResponseNode, SVGDrawNode).
Fixes rare problem reported by Elissa S where translated texts weren't appearing when an child node (e.g. ChallengeQuestionNode) was used in the project but not its parent (e.g. MultipleChoiceNode).