js: Move current_msg_list, home_msg_list to ES6 module message_lists.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

static/js/zulip_test.js

@@ -7,6 +7,7 @@ export {
     wildcard_mention_large_stream_threshold,
 } from "./compose";
 export {private_message_recipient} from "./compose_state";
+export {current as current_msg_list} from "./message_lists";
 export {get_stream_id, get_sub, get_subscriber_count} from "./stream_data";
 export {get_by_user_id as get_person_by_user_id, get_user_id_from_name} from "./people";
 export {last_visible as last_visible_row, id as row_id} from "./rows";