[GocadSGridReader] Removed unused method parsePropertiesFileName();
MeshLib::GocadNode used for storing FACE_SET information.
Changed handling of Gocad FACE_SET fundamental.

Used the MeshLib::GocadNode instead of storing the
FACE_SET information in arrays of struct FaceSet. In
consequence the interface of the class GocadSGridReader
changed, too.
Added FACE_SET info as property to mesh elements for visualization.