Add a registerNodeType function that allows to register a new node type.
This can be helpful during migration when we need to access a node type that has been changed or removed.
The script takes as parameter the name of the node type, and as an optional parameter, the namespace and the supertype.
The default value for the supertype is `unstructured`, in order to read/write/remove every attributes.
If the node type already exists, the node type is first unregistered.