Update glTF 2.0 models

Correct case in gltf2 example

ColladaLoader2: Refactoring animations

Update endOfContent method of FBXLoader binary parser

Light Helpers: prevent console warning from undefined color

Cloth Animation example: set shadowMap.renderSingleSided to false

... required in this case because the cloth is double-sided.

Add displacementMap support to distanceRGBA shader

BufferGeometry: refactor normalizeNormals()

- added gitter badge to readme per issue #11614

Clipping Intersection Example: Added plane helpers

Added overrideColor parameter to LightHelpers

WebGL clipping example: render shadows double-sided

WebGLShadowMap: Proper shadows when clipIntersection is true