Added `OsdUtilVertexSplit` which creates a vertex-varying data table by duplicating vertices in a `FarMesh`.  Catmark subdivision is supported.

* added public functions to `FarMeshFactory` that duplicate, rearrange, and split vertices
* added supporting protected functions to `FarCatmarkSubdivisionTablesFactory` and `FarPatchTablesFactory`
Merge pull request #333 from nathan-at-digitalfish/vertex_splitting

Vertex splitting