Fix linking of ObjectVisualizer plugin against VTK 6.0
Fix initialization of VTK with VTK 6.0

Without this the VTK core is not initialized and VTK will crash when
you try to use it in

See http://www.vtk.org/Wiki/VTK/VTK_6_Migration/Factories_now_require_defines
for details
Merge pull request #50 from danvratil/1.3

Looking good. Thanks a lot for the patch.