Names, where present, must be unique for each parent.
Node:
* String getName()
* void setName(String name)
* boolean isNamed()
NodeItem - replaces all constructor:
* (data)
* (data, name)
* (data, nameSupplier)
* (data, parent)
* (data, nameSupplier, parent)
The name supplier takes a node and generates a string at the time the node
is constructed. The root node has a default name supplier that returns null
which means that the node is considered unnamed. Other nodes may provide
their own name supplier that would be used be new nodes created within
their subtree.
