common.glsl: transformNormal -> transformDirection and inverseTransformNormal -> inverseTransformDirection.

Address @zz85's concern about using the constant 0.33333 insteaed of a division: https://github.com/mrdoob/three.js/pull/5785#discussion_r22146657

adopt common.glsl shader utilities across all shaders where applicable.  Fix vec*matrix bug in envmap_fragment.glsl

Aspirin model file updated

Conflicts:
	src/math/Ray.js

Conflicts:
	examples/webgl_decals.html

Updated the Aspirin PDB file to be chemically accurate, Fixes #5779.

StereoEffect - Modified to be an off-axis stereo effect