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/admin_console/system_users/system_users.jsx

@@ -1,3 +1,5 @@
+import PropTypes from 'prop-types';
+
 // Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
 // See License.txt for license information.
 
@@ -34,10 +36,10 @@ const USERS_PER_PAGE = 50;
 
 export default class SystemUsers extends React.Component {
     static propTypes = {
-        actions: React.PropTypes.shape({
-            getTeams: React.PropTypes.func.isRequired,
-            getTeamStats: React.PropTypes.func.isRequired,
-            getUser: React.PropTypes.func.isRequired
+        actions: PropTypes.shape({
+            getTeams: PropTypes.func.isRequired,
+            getTeamStats: PropTypes.func.isRequired,
+            getUser: PropTypes.func.isRequired
         }).isRequired
     }
 

webapp/components/admin_console/system_users/system_users_dropdown.jsx

@@ -13,13 +13,15 @@ import {adminResetMfa} from 'actions/admin_actions.jsx';
 
 import {FormattedMessage} from 'react-intl';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 
 export default class SystemUsersDropdown extends React.Component {
     static propTypes = {
-        user: React.PropTypes.object.isRequired,
-        doPasswordReset: React.PropTypes.func.isRequired,
-        doManageTeams: React.PropTypes.func.isRequired
+        user: PropTypes.object.isRequired,
+        doPasswordReset: PropTypes.func.isRequired,
+        doManageTeams: PropTypes.func.isRequired
     };
 
     constructor(props) {

webapp/components/admin_console/system_users/system_users_list.jsx

@@ -1,3 +1,5 @@
+import PropTypes from 'prop-types';
+
 // Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
 // See License.txt for license information.
 
@@ -16,17 +18,17 @@ import SystemUsersDropdown from './system_users_dropdown.jsx';
 
 export default class SystemUsersList extends React.Component {
     static propTypes = {
-        users: React.PropTypes.arrayOf(React.PropTypes.object),
-        usersPerPage: React.PropTypes.number,
-        total: React.PropTypes.number,
-        nextPage: React.PropTypes.func,
-        search: React.PropTypes.func.isRequired,
-        focusOnMount: React.PropTypes.bool,
-        renderFilterRow: React.PropTypes.func,
+        users: PropTypes.arrayOf(PropTypes.object),
+        usersPerPage: PropTypes.number,
+        total: PropTypes.number,
+        nextPage: PropTypes.func,
+        search: PropTypes.func.isRequired,
+        focusOnMount: PropTypes.bool,
+        renderFilterRow: PropTypes.func,
 
-        teamId: React.PropTypes.string.isRequired,
-        term: React.PropTypes.string.isRequired,
-        onTermChange: React.PropTypes.func.isRequired
+        teamId: PropTypes.string.isRequired,
+        term: PropTypes.string.isRequired,
+        onTermChange: PropTypes.func.isRequired
     };
 
     constructor(props) {