Remove unneeded function calls, rearrage for fused multiply–add, remove
excessive shader whitespace

add gamma GUI to webgl_shading_physical.html.  But it is slightly incorrect because the shaders are not properly recompiled upon gamma change.

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