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/delete_modal_trigger.jsx

@@ -1,3 +1,4 @@
+import PropTypes from 'prop-types';
 import React from 'react';
 
 import ConfirmModal from './confirm_modal.jsx';
@@ -67,5 +68,5 @@ export default class DeleteModalTrigger extends React.Component {
 }
 
 DeleteModalTrigger.propTypes = {
-    onDelete: React.PropTypes.func.isRequired
+    onDelete: PropTypes.func.isRequired
 };