(fwVTKQml): fix QML Tutos with VTK Scene

What does this MR do?

The Qml tutorials using VTK scenes doesn't work, the images and meshes are not displayed.

How to test it?

Launch:

• Tuto08GenericSceneQml
• fwQtTest
• PoCDialog

Data

some image or mesh

Some results

Additional tests to run

• works on linux
• works on windows
• works approximately on macos

Associated Issues/Merge Requests

• Issues

  • #305 (closed)

• Merge requests

  • !164 (merged)
  • !184 (merged)