Feature Request - Toggle subdirectories

I'd like a button added next to the "change directory" button that could toggles whether the sub-folders are included in the list of files. Clicking it would include/exclude the sub-folders and perform a refresh as well.

I like to group folders of similar music together for editing, such as several volumes of a series, but there are also many single folders. As I work I find that MP3TAG is in the "wrong" mode as I edit combinations of single folders and/or folders with subs. If I find I can't edit a collection easily as a batch but have to single out a particular folder, it would be great to just click to change the mode.

Thanks for considering this.