name option for items, so they can be accessed after copyGraph

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---

Right now there's no easy way to access a child of a parent copied with `copyGraph`.

``` js
// right arm
let upperArm = new Zdog.Shape({
//...
});
let foreArm = new Zdog.Shape({
addTo: upperArm,
// ...
});
// hand
new Zdog.Shape({
addTo: foreArm,
color: '#C25',
// ...
});

// left arm
upperArm.copyGraph();

// How do set the left hand to a different color?
```

With the `name` option, you could access children via an Object property.

``` js
// right arm
let upperArm = new Zdog.Shape({
//...
});
new Zdog.Shape({
addTo: upperArm,
name: 'foreArm', // accessible as parent.foreArm
// ...
});
// hand
new Zdog.Shape({
addTo: upperArm.foreArm,
name: 'hand', // accessible as parent.hand
color: '#C25',
// ...
});

// left arm
let leftArm = upperArm.copyGraph();

// set left hand to different color
leftArm.foreArm.hand.color = '#EA0';
```

The issue identifies copyGraph as the entry point and shows the intended parent.foreArm and leftArm.foreArm.hand access pattern; start by tracing that API and its child-copy behavior. Done means named descendants remain accessible on the copied graph and the demonstrated hand-color change works, with coverage for this behavior.

Written by the indexing model from the issue text.