Implemented CellAttributes interface in Cell class. Fixed requireValid macro & associated common test method. Added LineWidth implementation & tests. Updated CellColor, LineStyle & DisplayStyle enumerations & tests to report valid minimum & maximum values. Some minor other import fixes.
Refactored reading of the CellColor, DisplayStyle, LineStyle & LineWidth classes. Added basic JointType class and updated Joint classes.
Added JointData class. Added readBool method to CellScene class. Refactored BoundingBox read into a separate class.  Refactored CellFlags read into CellFlags.