Question regarding JupyterLab Widgets

Thank you so much for this work! We've been looking for a quick way to develop/debug JLab extensions for quite some time now, and this seems to be of great help!

I have a question regarding JupyterLab widgets, particularly those that subclass `@lumino/widgets`. Simply put, if we use the

As a barebone example, I was trying to see if it'd be possible to dynamically load the tutorial widget/extension (https://github.com/jupyterlab/jupyterlab_apod).

So in this case, the index.js of the APOD Widget/Extension compiles into something like
```
define(["require", "exports", "@jupyterlab/application", "@jupyterlab/apputils", "@lumino/widgets"], function (require, exports, application_1, apputils_1, widgets_1) {
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
;
class APODWidget extends widgets_1.Widget {
...
}

function active(app, palette, restorer) {
}

/**
* Initialization data for the jupyterlab_apod extension.
*/
const extension = {
id: 'my-apod-extension',
autoStart: true,
requires: [apputils_1.ICommandPalette, application_1.ILayoutRestorer],
activate: activate
};
exports.default = extension;
```

And I tried to create a JS file which looks like
```
return function()
{
return {
id: 'dynext-test-extension',
autoStart: true,
requires: ["jupyter.extensions.jupyterWidgetRegistry"],
activate: function(app, widgets) {
require.config({
// take the widget from `unpkg.com`
baseUrl: "/Users/tingkailiu/Projects/FFBO/JLab2/dynext-test-extension/lib"
});

let widget = "index";
// note that we are using require js here to load the AMD module
// requirejs is automatically loaded with jupyterlab-dynext.
// * (star) selects the latest version from unpkg, and then loads the `/dist/index.js` file
// the final URL will be something like https://unpkg.com/bqplot@^0.5.2/dist/index.js
require([widget], function(plugin) {
widgets.registerWidget({
name: widget,
version: plugin.version,
exports: plugin
});
});
}
};
}
```

But it seems like `jupyter.extensions.jupyterWidgetRegistry` is not found and it's because I'm not using `jupyterlab-manager` since I'm trying to load a lab widget instead of a ipywidget.

Could you suggest a way for dynamically loading and developing jupyterlab widget/extension?