Fix problems with multiple WiVis widgets

[hendrikverdonck]

If multiple WiVis widgets are requested either:

• The mayavi primitives are plotted in the same scene. This problem only exists for the WiVis PointCloud and VectorField tvtk_primitives, the CoordSystem primitive is plotted in the correct scene. This problem can be fixed by setting the mayavi_scene explicitly when calling points3D and quiver3d in tvtk_primitives.

• With the fix for problem 1, the primitives are plotted in the correct scene, but the controls are sometimes not correctly connected.

  • Works: selecting two markers and clicking make modal visualization
  • Works: making modal visualization, stopping the visualization, closing the docks, making new visualization
  • Does not work: opening a new visualization when another is already open
  • Works: closing a dockwidget if a visualization was still running and opening a new visualization