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/loading_screen.jsx

@@ -3,6 +3,8 @@
 
 import {FormattedMessage} from 'react-intl';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 
 export default class LoadingScreen extends React.Component {
@@ -44,6 +46,6 @@ LoadingScreen.defaultProps = {
     position: 'relative'
 };
 LoadingScreen.propTypes = {
-    position: React.PropTypes.oneOf(['absolute', 'fixed', 'relative', 'static', 'inherit']),
-    message: React.PropTypes.node
+    position: PropTypes.oneOf(['absolute', 'fixed', 'relative', 'static', 'inherit']),
+    message: PropTypes.node
 };