Initial simple implementation of the RigidBody message without interpolation.
Treat unknown local assets as "not found" (fail transfer) instead of always going the "requests to sources outside registered LocalAssetStorages have been forbidden" (no transfer created at all) route, unless the ref is absolute local path.
Error dependent assets if a dependency fails to load. Use the error material consistently in Mesh, Sky & Terrain, but only when the command line option --useErrorAsset is specified. Otherwise the failing material is left blank (default.)
Code cleanup.