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/create_comment.jsx

@@ -30,6 +30,7 @@ const ActionTypes = Constants.ActionTypes;
 const KeyCodes = Constants.KeyCodes;
 
 import {REACTION_PATTERN, EMOJI_PATTERN} from './create_post.jsx';
+import PropTypes from 'prop-types';
 import React from 'react';
 
 export default class CreateComment extends React.Component {
@@ -659,7 +660,7 @@ export default class CreateComment extends React.Component {
 }
 
 CreateComment.propTypes = {
-    channelId: React.PropTypes.string.isRequired,
-    rootId: React.PropTypes.string.isRequired,
-    latestPostId: React.PropTypes.string
+    channelId: PropTypes.string.isRequired,
+    rootId: PropTypes.string.isRequired,
+    latestPostId: PropTypes.string
 };