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/user_settings/user_settings_theme.jsx

@@ -21,6 +21,8 @@ import {FormattedMessage} from 'react-intl';
 
 import {ActionTypes, Constants, Preferences} from 'utils/constants.jsx';
 
+import PropTypes from 'prop-types';
+
 import React from 'react';
 
 export default class ThemeSetting extends React.Component {
@@ -353,8 +355,8 @@ export default class ThemeSetting extends React.Component {
 }
 
 ThemeSetting.propTypes = {
-    selected: React.PropTypes.bool.isRequired,
-    updateSection: React.PropTypes.func.isRequired,
-    setRequireConfirm: React.PropTypes.func.isRequired,
-    setEnforceFocus: React.PropTypes.func.isRequired
+    selected: PropTypes.bool.isRequired,
+    updateSection: PropTypes.func.isRequired,
+    setRequireConfirm: PropTypes.func.isRequired,
+    setEnforceFocus: PropTypes.func.isRequired
 };