More informative error messages when creating sunburst charts

[chriddyp]

When dealing with larger datasets, it can be tricky to validate the shape & form of sunburst data. It would be helpful if the console error messages let us know some more info about our malformed datastructure.

For example, updating:

WARN: Multiple implied roots, cannot build sunburst hierarchy.

To be more like:

WARN: Multiple implied roots, cannot build sunburst hierarchy. These roots include x, y, z.

cc @nicolaskruchten