Consistency with IPyWidget

[AntoinePrv]

This issue is meant to track the evolution of the consistency with IPyWidget.

• Update JS libraries versions
  • Update declared versions Fix and update widget attributes #239
  • Test for missing attributes Fix and update widget attributes #239
  • Update widget attributes Fix and update widget attributes #239
  • Implement missing styles Add missing styles #243
  • Add missing visual attributes: "description", "description_allow_html", "tabbable", "tooltip" Add visual properties #242
  • Test missing attributes schemas
• Update protocol version Update to protocol 2.1.0 (echo_update) #251
  • Update declared version
  • Implement echo_update feature
• Update packaging dependency to jupyterlab_widgets