Resolve default export warnings from Webpack

Webpack was printing several warnings about missing default exports,
particularly from components, where we auto-generate a default import via the
component index.

As part of this, the emoji picker recent handling (which is not a component) is
moved elsewhere to avoid the generated import.

src/components/views/context_menus/TopLeftMenu.js

@@ -27,7 +27,7 @@ import {MatrixClientPeg} from '../../../MatrixClientPeg';
 import {MenuItem} from "../../structures/ContextMenu";
 import * as sdk from "../../../index";
 
-export class TopLeftMenu extends React.Component {
+export default class TopLeftMenu extends React.Component {
     static propTypes = {
         displayName: PropTypes.string.isRequired,
         userId: PropTypes.string.isRequired,