GLTFLoader: only refresh uniforms on correct material

GLTFLoader: Remove old or unstable extensions.

Added WebGL spec link to WebGL renderer docs

Updated Rollup to ^0.55.1

This has been added to help explain what 'powerPreference' does.

Matrix4 - fix documentation on matrix and matrixWorld

Update google-closure-compiler

WebVR.js: Automatically enter VR on vrdisplayactivate event.

Matrix4 - description for matrix and matrixWorld items in  #13183

Simple case: 
1. Load GLTF File with Specular-Glosiness-Material so the ```refreshUnfiorms``` function is being set ```mesh.onBeforeRender = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].refreshUniforms;``` 
2. Use an override material for the scene to render, for example use the SAOPass.
3. Get error because u try to work with uniforms of a material which doesn't have any

Suggestion:
Simple check if the material has the property ```isGLTFSpecularGlossinessMaterial``` and it is true. Because the ```refreshUniforms``` function is only set if it is true.

Change incorrect references in Torus docs

WebGLRenderer: Fix first time skin render

Fixed vulnerable dev-dependency (serve)

  The tube parameter is actually a radius, not a diameter

Editor: Moved grid to settings.

WebGLRenderer: Removed .setFaceCulling()

GLTFExporter: Morph Target weights support

Propagate VR-mode upon link traversal so the the user doesn't have
to manually click on the 'enter VR' button each time.