[Low Priority] Simple Interactive Preview

[PearCoding]

Add simple interactive preview raytracer for first impression on material and data.
Keep complex specular and diffuse interaction at minimum. (e.g. only ~4 specular and ~1 diffuse bounce)

-- Requires GPU utilization for fast response.
-- Iterative pixel sampling with only one pixel sample each step.

[PearCoding]

This also requires improved scene loading -> Should be done in advance.