frontend: Add basic user_status module.

So far this processes page_params, but it's otherwise
an unused internal API.

static/js/ui_init.js

@@ -297,6 +297,7 @@ $(function () {
     }
     server_events.initialize();
     people.initialize();
+    user_status.initialize();
     compose_pm_pill.initialize();
     search_pill_widget.initialize();
     reload.initialize();