- modified ISurface to be pure abstract base (interface)
      - changed method signatures 
   - added IMaterial as pure abstract base (interface)
   - moved Surface from DDCore to DDRec
     - classes VolSurface (VolPlane, VolCylinder) implement ISurface
     - implement insideBounds using volume
 - changed Vector3D to be copy of gear::Vector3D (slightly improved)