Collapsible File Display

The 'files' tab on selecting a Torrent needs to to have a collapsible directory structure, so that you can easily select ( or deselect) directories for download without having to scroll down through all the files (and subdirectories, with their files) in between.

Since the download selection is already controlled by dedicated checkboxes, it's probably easiest to make the directories themselves 'clickable' tap to expand, tap again to collapse.