unread_banner: Group all unread banners up into a folder.

Since we currently have 3 unread banners, it'd be much preferred to group
all of them up into one folder to keep them organized like how compose
banners are. This way, it's much easier to keep track of unread banners
and new ones in the future.

web/src/unread_ui.js

@@ -1,8 +1,8 @@
 import $ from "jquery";
 
-import render_mark_as_read_disabled_banner from "../templates/mark_as_read_disabled_banner.hbs";
-import render_mark_as_read_only_in_conversation_view from "../templates/mark_as_read_only_in_conversation_view.hbs";
-import render_mark_as_read_turned_off_banner from "../templates/mark_as_read_turned_off_banner.hbs";
+import render_mark_as_read_disabled_banner from "../templates/unread_banner/mark_as_read_disabled_banner.hbs";
+import render_mark_as_read_only_in_conversation_view from "../templates/unread_banner/mark_as_read_only_in_conversation_view.hbs";
+import render_mark_as_read_turned_off_banner from "../templates/unread_banner/mark_as_read_turned_off_banner.hbs";
 
 import * as activity from "./activity";
 import * as message_lists from "./message_lists";