"All Additional Files" (etc) should show descriptions

[towerofnix]

Descriptions may provide key information to do with particular files (especially via hsmusic/hsmusic-data#19). Since they're meant to be brief to begin with, it shouldn't be a usability inconvenience to show them in this listing, too.

[towerofnix]

Currently additional files are only expandable if they contain multiple files. Might have to adopt the standard additional file layout for every item, so weigh that in terms of usability — it's probably fine if not better, but worth a closer look.