Add functionality to display ImgLabelings

When running e.g. `ops.run("labeling.cca", input)` in a notebook, it would be nice to have a simple way to display the resulting `ImgLabeling`. Let's add this to `DefaultNotebookService`:

```groovy
indexImage = labels.getIndexImg()
indexImage.firstElement().setReal(255.0) // hack to get full 0-255 display range

view = ij.imageDisplay().createDataView(indexImage)
view.rebuild()
lut = ij.lut().loadLUT(new File("luts/glasbey_inverted.lut"))
view.setColorTable(lut, 0)
view.rebuild()
view
```

maybe with an optional `ColorTable` input?

`display(ImgLabeling labels)`
`display(ImgLabeling labels, ColorTable lut)`

Start in DefaultNotebookService and inspect its existing display entry points and the ImgLabeling API used by ops.run("labeling.cca", input). Reproduce the notebook case, then verify that display(ImgLabeling) renders the label image and that the optional ColorTable overload applies the requested LUT; confirm the result interactively in a notebook.

Written by the indexing model from the issue text.