Reimplement vtkVRMLExporter with C++ streams

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

Currently, vtkVRMLExporter can't be used to serve web pages without the extra steps of writing out and reading back a temporary file.

By using C++ streams, you have the option of writing to a file or writing to a string buffer, in which case, the client can get the VRML text by calling a method on the object.

I have already modified the class to do this. Feel free to use it, if you'd like.