lasso node example

[FrissAnalytics]

Hi Vasco,

Hope you are doing well! This PR adds an example that shows how nodes can be selected via a lasso selection.

The example is based on this example by Fil on observablehq.
Nodes can be selected by holding shift and making a drag move.
The lasso selection boundary is depicted as a grey polygon drawn behind the nodes using onRenderFramePre
Selected nodes are depicted in orange and have fixed x and y positions after lasso selection
The graph can be panned and zoomed with the selection.
To clear the selection, hold shift and click without dragging

Hope this is helpful to others!

Kind regards, Herman