#2 wviz warning when WebGL is not supported

[Bener Suay]

Patrick Goebel from PiRobot gave wviz a try but couldn't get it running. It turns out his machines don't have the hardware to support WebGL. Wviz should catch the following spiderGL error and help user understanding what's wrong:

"spidergl.js:7502Uncaught Error: SpiderGL : Cannot get WebGL context
_SglCanvasManagerspidergl.js:7502
_sglManageCanvasspidergl.js:7885
sglRegisterLoadedCanvasspidergl.js:7910"

Reference:
http://answers.ros.org/question/43381/wviz-missing-visualization-control-panel-button/