Tests AffineMatrix3D is only rotation and translation.

[CnlPepper]

At present we don't have any utilities to determine what an AffineMatrix3D describes. It is possible to check of a matrix defines a valid translation and rotation, which is essential if decomposing a matrix.

Shear, scaling, reflections are all forbidden operations in raysect (no enforced for speed, by convention). A test that checks a matrix does not contain these elements would also be useful.