Add utf8 everywhere

I'm having another crack at this by using KWSYS and setting the default encoding to UTF8 in cmake. Opening files and file streams are altered so that file/folder names are properly handled by Windows.

Some VTK readers return ifstream objects from their OpenFile() methods however I think they should probably just be istream objects. I have retained the syntax but is it really necessary that a descendant class or third party is able to close the file stream?

@ben.boeckel Please review. The code won't compile until some minor changes are merged into KWSYS for ifstream/ofstream.