Alter model in preparation of implementing enhancement #7.

The new model allows trees of items to be created. Basic wardrobe functionality will only need a single parent-child relationship, but I figure that this might be easily expanded in the future.
Check that no error is generated.
Load generic item v2 meshes with new version number and without tangents

The simplest possible solution right now. I have no idea how to tell
whether a file has tangents, so I assume that all new-style files have
no tangents. That is not optimal. This is all preparation work to
implement #7.