Convert CommonJS exports to ES6-compatible exports

We use `export default` begrudgingly here. Ideally we'd use just `export`, though this entire SDK expects things to be exported as a default. Instead of breaking everything, we'll sacrifice our export pattern for a smaller diff - a later commit can always do the default export -> regular export conversion.

src/components/views/messages/TextualBody.js

@@ -35,7 +35,7 @@ import {IntegrationManagers} from "../../../integrations/IntegrationManagers";
 import {isPermalinkHost} from "../../../utils/permalinks/Permalinks";
 import {toRightOf} from "../../structures/ContextMenu";
 
-module.exports = createReactClass({
+export default createReactClass({
     displayName: 'TextualBody',
 
     propTypes: {