Improve introduction doc fixing small scope issues

Small issues:
- Missing `var` keywords
- Multiple left-hand assignments declaring global variables, more info: http://stackoverflow.com/questions/1758576/multiple-left-hand-assignment-with-javascript

Fix Adaptive Tone Map issue on very dark (initial) scene

fix comparison with -0 in Math.js

fix operator precedence bug in WWOBJLoader2.js

Examples: Clean up

WebVR: Update origin trial token

Editor: Removed references to SceneLoader

OrbitControls: clean up

[glTF] Enable vertex colors on materials.

Update material.py

[examples] Remove unused lines from webgl_postprocessing_outline.html

Blendmesh example without alerts

Optimized version of LTC Area lights

When last luminance is zero and time delta also very small,
chances are that the output luminance is still zero on the
next run, even when current luminance is rather high. The
reason behind is that luminance value is stored on the red
channel of a 1x1 texture. Therefore computed values below
~0.002 get rounded down to zero again (1/255 => ~0.004).

This could lead to a division by zero in the ToneMapShader.
Added `minLuminance` option to avoid this edge case.

There is also no reason to write to all color channels when
only the red channel is used (ToneMapShader uses red too).

Additionally implements `renderToScreen` composer flag.

Fixed blender  not export the material's opacity

SpotLightShadow: Fixed #11158

Rename JOINT->JOINTS_0, WEIGHT->WEIGHTS_0.

FIX IE11 shader compilation - use more selective whitespace matching

Blendmesh example newly implemented

Docs: AnimationMixer.html - fix alphabetical method order