Move to common all libs shared by demos like J3DI, J3DIMath, gl-matrix, ...

...webgl-utils and webgl-debug

Issue #66

Deleted:
    SmallPathTracing/gl-matrix.js
    VideoCube/BasicVideoCube.html
    VideoCube/J3DI.js
    VideoCube/J3DIMath.js

Modified:
    * SmallPathTracing/webcl-smallpt.html
    * SmokeVision/fluid.html
    * VideoCube/VideoCube.html

Moved:
    * SmokeVision/J3DI.js -> common/J3DI.js
    * SmokeVision/J3DIMath.js -> common/J3DIMath.js
    * SmokeVision/gl-matrix.js -> common/gl-matrix.js
    * SmokeVision/webgl-utils.js -> common/webgl-utils.js