[WIP] Fix build errors

[pbugnion]

As far as I can tell, master has stopped building correctly due to a dependency update (related to this?). This is (probably) only visible off a fresh clone, or at least removing the node_modules in jupyter-widgets-controls. It also occurred on PR #1410.

I think this is due to an update in the type defintions for JQuery. The module definition now reads:

declare module 'jquery' {
    export = factory;
}

declare function factory(window: Window, noGlobal?: boolean): JQueryStatic;

declare const $: JQueryStatic;

This means that the only ways of importing jquery are:

const $ = require('jquery') // uses the exported module 'jquery'
import 'jquery' // uses the global exports, which injects $ into the global namespace

In particular, we were importing jQuery using import * as $ from 'jquery', which is now not allowed.

This is still fairly broken on Travis.

[maartenbreddels]

I cannot install ipywidgets at all, also not previous versions. I'll try this fix.

[jasongrout]

This indicates this will be fixed soon: DefinitelyTyped/DefinitelyTyped@844920f#commitcomment-22611629

[jasongrout]

The import errors are fixed. If you want to remove your import changes, I'll merge - the es2015.iterable changes still look needed.

[pbugnion]

Ah thanks for checking! I'll do this now.

[jasongrout]

I added the same fix to jupyter-widgets-base. Thanks!