Issues with jupyter 4.0

[garrison]

It looks like the syntax for loading modules has changed again in jupyter 4.0:

$([IPython.events]).on("app_initialized.NotebookApp", function () {
    require(['base/js/utils'], function(utils) {
        utils.load_extensions('notify');
    });
});

After fixing this, the notebook and extension load correctly, but I still don't see the notification permissions in the toolbar. Actually, now everything seems to work once I change custom.js as mentioned above.

[sjpfenninger]

This is addressed by a much simpler way to load extensions as described in 6ad96d0.