Update rendering logic

[trungleduc]

This PR improves the widget rendering logic, the create_viewer and the render_viewer method now work independently. There are 2 scenarios:

• If create_viewer is called before render_viewer, the create_viewer will create empty outputs, and render_viewer will fill these outputs with the real widget.
• If render_viewer is called before create_viewer, the render_viewer will create the real widgets, and create_viewer will create outputs filled with widgets.

[github-actions[bot]]

:point_left: Launch a Binder on branch trungleduc/glue-lab/render-logic