Updating client dependencies. Switching to yarn. (#6433)

* Updating client dependancies. Switching to using yarn.

* Updating React

* Moving pure components to using function syntax (performance gains with newer react version)

* Updating client dependancies.

* Ignore .yarninstall

* Enabling pre-lockfile because it's the entire point of using yarn.

* Removing old webpack config

* Moving to new prop-types

* Fixing ESLint Errors

* Updating jest snapshots.

* Cleaning up package.json

webapp/components/message_wrapper.jsx

@@ -5,6 +5,8 @@ import * as TextFormatting from 'utils/text_formatting.jsx';
 import * as Utils from 'utils/utils.jsx';
 import {getSiteURL} from 'utils/url.jsx';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 
 export default class MessageWrapper extends React.Component {
@@ -35,6 +37,6 @@ MessageWrapper.defaultProps = {
     message: ''
 };
 MessageWrapper.propTypes = {
-    message: React.PropTypes.string,
-    options: React.PropTypes.object
+    message: PropTypes.string,
+    options: PropTypes.object
 };