Camera only rotates when model is on the top render layer

[thompson318]

In GitLab by @ThomasDowrick on Mar 22, 2019, 08:49

We are using multiple render layers in VTKOverlayWindow self.GetRenderWindow().SetNumberOfLayers(3) for background, generic overlay stuff (e.g. text) and models.

The models are currently on layer 1, but it turns out they need to be on the topmost layer (2) in order for the camera rotations to work properly.