Copy paste lacing issue fix

This is a fix for error : http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-117


Changed the base "SaveNode()" and "LoadNode()" functions to now save the Lacing,Preview and PreviewUpstream also. To ensure it is called from every node, have added the base.SaveNode() and base.LoadNode() to every overriden function of Save/LoadNode.

Also changed the ReadEnum of the XmlElementHelper class as the if() statement was incorrect.