ex05: small correction for draw_rays() [fix]
ex05: rename some local vars to not conflict with global ones
ex05: an other try at create_primary_rays()

uses some cheating(?) (in world_display()),
but otherwise looks good.
ex05: add two debug helper functions

* extractTransformationPart(const mat4& transMat)
* printMat(const mat4& myMat)