PictureFlow: Add ability to insert into playlists

Songs or albums can now be added to new or
existing playlists directly from PictureFlow.

Change-Id: I6ea27e393fee0d5688385f9e91cf835be1756a7a

apps/plugin.c

@@ -824,6 +824,7 @@ static const struct plugin_api rockbox_api = {
     splash_progress,
     splash_progress_set_delay,
     fix_path_part,
+    onplay_show_playlist_cat_menu,
 };
 
 static int plugin_buffer_handle;