No more NullPointerExc. with Blinn scene
Correct handling of shadow acne
Fixed CSGCylinder and Cone. Added UnitCylinder.
Some minor changes in constructors, temporary changes in scenes
Implemented XYZGrid
Fixed CSGInstance
Hardly simplified computation of normals for cone. Have a look, @panmari

This should work since the canonic cone is based on x^2 + y^2 = z^2.
This leads to an 'inner angle' of 90deg. Imagine a simple example in 2D with the equation x^2 = y^2.