ENH:  Added Unicode mode to vtkDelimitedTextReader.  The reader currently supports UTF8 and UTF16 in Unicode mode.  The behavior of the reader with respect to ascii or unicode input is controlled by the SetUnicodeCharacterSet() method.  By default (without calling SetUnicodeCharacterSet()), the reader will expect to read ascii text and will output vtkStdString columns.  Use the Set and Get methods to set delimiters that do not contain UTF8 in the name when operating the reader in default ascii mode.  If the SetUnicodeCharacterSet() method is called, the reader will output vtkUnicodeString columns in the output table.  In addition, it is necessary to use the Set and Get methods that contain UTF8 in the name to specify delimiters when operating in unicode mode.