Show error message when no visuals are renderable

[kd-ods]

Buried in this issue #70, was a requirement that:

When data is a valid JSON array of objects, but - after parsing and processing - actually no nodes or edges are rendered. It would be good to give user feedback in that instance. A simple error message like this would be useful:

Your data does not have any information that can be drawn.

Test data

[
  {
    "name": "nothing"
  }
]