JavaScript support for Voxels.findRayIntersection()

* Adds ability for JS to get voxel intersected by the pick ray closes #1908 
* adds new Voxels.findRayIntersection(pickRay) - which returns the voxel details for the voxel that intersects the ray in question
* adds some example scripts to demonstrate how to use this API, including one that "adds" a voxel to the clicked face of a voxel (similar to our C++ voxel editing tools)