Cleanup test warnings

[jasonLaster]

When we converted to React 15.6 we started seeing some createClass test warnings:

  Warning: Accessing PropTypes via the main React package is deprecated, and will be removed in  React v16.0. Use the latest available v15.* prop-types package from npm instead. For info on usage, compatibility, migration and more, see https://fb.me/prop-types-docs

It would be great to clean those up.

[joel-bentley]

It looks like these warnings are from a known issue in React v15.6 when using import * as React from 'react';
facebook/react#10583

The React team decided not to fix since these warnings go away when switch to React v16.0

[joel-bentley]

So, the above is the case in only one instance src/components/shared/Modal.js

The rest of the errors are from React.createClass and React.PropTypes being used in the

devtools-launchpad
devtools-splitter
devtools-components

packages, which are part of https://github.com/devtools-html/devtools-core. I could make a PR over there.

[jasonLaster]

@joel-bentley thanks that would be great