BUG: Update the WebGLExport module to use release 9 of XTK.

The generated XTK code is now compatible with the slightly new API and linking against the tag of release 9 should ensure stability in the future.



git-svn-id: http://svn.slicer.org/Slicer4/trunk@21567 3bd1e089-480b-0410-8dfb-8563597acbee