niflib: Update to match nif.xml.  Replace Float4 with Vector4.  Use Vector4 in bhk objects.  Introduce default values for array types.

syncing niflib with xml (note: Union field missing from BoundingVolume; see niflib hack in docsys/nifxml.py)

Add helper method to ControllerSequence which allows for adding item by name and not with target attached.

Update UpdateTangentSpace to match nifskope and add my algorithm adapted from the Obsidian developers version.

   - Fix issue with exporting Skin data causing missing vertexes in nifskope
   - add helper methods for collision related export.
   - fix crashes when exporting animation