Example for events with ngraph.three

Hi,
Again nice work (like Vivagraph) !
Have you an example to show how events works in with threejs render [like with for Vivagraph](https://github.com/anvaka/VivaGraphJS/blob/master/demos/other/webglInput.html#L31-L41)?
Thanks :)

Start by reading the linked VivaGraphJS demo at demos/other/webglInput.html#L31-L41 and inspect the ngraph.three examples or entry points available in the repository. Done means a threejs-rendered graph example demonstrates how event handling works, comparable to the referenced VivaGraph example.

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