Geometric selection node

[trisyoungs]

Describe the feature / issue
A useful addition to the generator nodes roster would be a GeometrySelect node which selects sites based on coordination / proximity of other sites, but calculates and passes on the geometry formed by those matching sites to its ForEach loop. This would allow for other yet-to-be-written nodes to, for instance, add new molecules at specific positions or rotations relative to that site.