Convert imports to ES6 from CommonJS

This is needed because `require()` means something different in webpack - it ends up importing the module as something we didn't expect (and is occasionally async)

src/async-components/views/dialogs/EncryptedEventDialog.js

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-const React = require("react");
+import React from "react";
 import createReactClass from 'create-react-class';
 import PropTypes from 'prop-types';
 import { _t } from '../../../languageHandler';

src/async-components/views/dialogs/keybackup/CreateKeyBackupDialog.js

@@ -17,7 +17,6 @@ limitations under the License.
 
 import React from 'react';
 import FileSaver from 'file-saver';
-
 import * as sdk from '../../../../index';
 import {MatrixClientPeg} from '../../../../MatrixClientPeg';
 import { scorePassword } from '../../../../utils/PasswordScorer';