gDiff for JSONNode utterly broken
With https://gitlab.science.ru.nl/clean-and-itasks/iTasks-SDK/issues/19#note_49734 I realized that clean-test's gDiff for JSONNode is utterly broken. Added/removed values are not indented properly. This is probably not possible, because you cannot recognize whether a JSON array is the representation of an ADT or of a list. Probably we should just resort to the derived version.