3D Scene not created if 3D model is added to a 2D scene

A 3D scene should be created when user adds a 3D model to a  2D scene (see QDS-1085). As it is now, 3D scene is not created when 3D model is added for example by dragging and dropping it to the navigator. User must know that view3D has to be added first to create a 3D scene to which the model can then be added.

Test steps:

Create a project

Import Quick3D

Drag and drop a Cube to the navigator -> Cube is created but not inside a 3D scene so it is not visible either in the form editor or the 3D Edit View.