refactor: make context.tsx tree-shakeable (#573)

- `components/` is not tree-shakeable, so importing it makes this file also not tree-shakeable
  - similar to my PR upstream and for the Storybook here to use individual imports

Signed-off-by: Anton Gilgur <agilgur5@gmail.com>

src/context.tsx

@@ -1,6 +1,8 @@
 import * as H from 'history';
-import { match} from 'react-router';
-import { NotificationsApi, PopupApi } from './components';
+import { match } from 'react-router';
+
+import { NotificationsApi } from './components/notifications/notification-manager';
+import { PopupApi } from './components/popup/popup-manager';
 
 export interface AppContext {
     router: {