A pure virtual function error was caused by a recent change that used metadata...

A pure virtual function error was caused by a recent change that used metadata for storage of the palette normalization mode.  Use of the CaretMappableDataFile's copy constructor resulted in a call to the virtual function getMetaData() for copying of the palette normalization mode.  This copying of the palette normalization mode has been removed and was probably unnecessary since the file metadata (that contains the palette normalization mode) should be copied by the file's copy constructor.