From spheres to cubes

[tristandeborde]

We want to make our raytracer compute intersections with cubes instead of spheres.
We need:

• A cube class (there's a sphere class from the code we can inspire ourselves from)
• To modify the render function to compute intersections with cubes
• To correct the straight line artifact on the output image!

• Easy way is with AABB, since Octree's voxels are axis-aligned = https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-box-intersection
• But for the physics and rasterization, the gamr voxels are OBB (not axis aligned) = http://www.opengl-tutorial.org/miscellaneous/clicking-on-objects/picking-with-custom-ray-obb-function/