Graph model plus opencascade
A prototype graph-based model resource and example session.
- The example session exposes OpenCASCADE (OCC) shapes as a component type. It supports importing native OCC models as well as IGES and STEP files.
- This commit also makes geometry::Cache::visit() run thread-parallel on cache entries. As a result, vtkResourceMultiBlockSource has some changes to make its visitor thread-safe.
- There are additional commits that make the ParaView extensions more friendly to resources that do not inherit model, mesh, or attribute resources.