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/select_team/components/select_team_item.jsx

@@ -1,3 +1,5 @@
+import PropTypes from 'prop-types';
+
 // Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
 // See License.txt for license information.
 
@@ -10,10 +12,10 @@ import * as Utils from 'utils/utils.jsx';
 
 export default class SelectTeamItem extends React.Component {
     static propTypes = {
-        team: React.PropTypes.object.isRequired,
-        url: React.PropTypes.string.isRequired,
-        onTeamClick: React.PropTypes.func.isRequired,
-        loading: React.PropTypes.bool.isRequired
+        team: PropTypes.object.isRequired,
+        url: PropTypes.string.isRequired,
+        onTeamClick: PropTypes.func.isRequired,
+        loading: PropTypes.bool.isRequired
     };
 
     constructor(props) {

webapp/components/select_team/select_team.jsx

@@ -14,13 +14,15 @@ import {Link} from 'react-router/es6';
 
 import {FormattedMessage} from 'react-intl';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 import logoImage from 'images/logo.png';
 
 export default class SelectTeam extends React.Component {
     static propTypes = {
-        actions: React.PropTypes.shape({
-            getTeams: React.PropTypes.func.isRequired
+        actions: PropTypes.shape({
+            getTeams: PropTypes.func.isRequired
         }).isRequired
     }