8 maintenance

- FromMayaMeshConverter checks stParameter and extraSTParameter values before looking up UVs. 

- PointSmoothSkinningOp handles faceVarying normals. Normals and Vertices must be the same length only if primitive is not a mesh. Also added a referenceIndices parameter that matches each vertex index from the input mesh to an index in the smooth skinning data. If empty, use full data from smooth skinning data. Updated PointSmoothSkinningOp test.