[Feature] Usage of surface normals on Gaussian Splats

[Crezle]

As a continuation on PR #286, I've been looking into including surface normals to gaussian splats for representing "brightness" effects from lightsources on splats (which is currently not supported).

Currently, without access to .PLY files with non-zero values for normals, I am unable to debug this but would be a great addition as other objects such as meshes are able to "react" to light sources.