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/file_attachment.jsx

@@ -7,6 +7,8 @@ import * as Utils from 'utils/utils.jsx';
 
 import {Tooltip, OverlayTrigger} from 'react-bootstrap';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 
 export default class FileAttachment extends React.Component {
@@ -172,13 +174,13 @@ export default class FileAttachment extends React.Component {
 }
 
 FileAttachment.propTypes = {
-    fileInfo: React.PropTypes.object.isRequired,
+    fileInfo: PropTypes.object.isRequired,
 
     // the index of this attachment preview in the parent FileAttachmentList
-    index: React.PropTypes.number.isRequired,
+    index: PropTypes.number.isRequired,
 
     // handler for when the thumbnail is clicked passed the index above
-    handleImageClick: React.PropTypes.func,
+    handleImageClick: PropTypes.func,
 
-    compactDisplay: React.PropTypes.bool
+    compactDisplay: PropTypes.bool
 };