Use the standard dicom backslash delimeter rather than pipe

When multiple strings are concatentated in DICOM files, they
use the backslash, so expose the same convention here for
consistency.

Libs/DICOM/Core/ctkDICOMDataset.cpp

@@ -446,7 +446,7 @@ QString ctkDICOMDataset::GetAllElementValuesAsString( const DcmTag& tag ) const
     }
   }
 
-  return qsl.join("|");
+  return qsl.join("\\");
 }