Glsl improvements

TO DO: *NeedsUpdate, CustomAttributes, Skinning, MorphTargets.

Fix for Firefox WebVR

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

Clean up phong shader

Add depth function to materials

Reuse program when not changed

Add and remove semicolons

Fixes #6266

Resuse program if code is the same and material updated

CanvasRenderer: typo

Remove the camera animation so that HMD orientation is applied correctly
and add a crosshair instead of mouse-based intersection.

This fixes things for Firefox since the latest builds include both an
Oculus device and a Cardboard device, even if you're on a desktop PC.

Added Gamma Correction Shader

Unnecessary parameter

Detach was taking a parameter that wasn't used. Removing it.

Lazy loading of variables in Matrix4