Revision 71

Conversion of ExtendedData to Managed/Native:
** Move into their own methods, so they can be re-used by all classes
   that need ExtendedData Marshalled to Managed/Native Data.
** Implement Editing ExtendedData for:
    *Art Tool Info
    *Exporter Info
    *Textures
    *Materials
** Fix error in ExtendedDataWrapper, when no extendedData exists -
    * Set MeberCount -> 0 [if == 0], instead of -1 (i.e. MemberCount - 1).