not to be merged yet

This changes how notebooks are loaded in order to fix a problem with large notebooks that somehow overloads the JS engine trying to start the plugins and render the notebook at the same time, resulting in a crashed document.

This PR solves the problem by completing the plugins before rendering the notebook.  The downside of this is that the notebook is not visible while you wait for the plugins to load, the page is pretty much empty (except for the menus at top which should be removed too since they could cause problems).

I am going to try a different approach, of rendering the notebook first.