[Tails-dev] Trash on persistent volume

As pointed out in a Whisperback report, there is currently no way of
emptying the trash stored in the persistent volume without interacting
with hidden files. I think that's an important usability issue.

When deleting a file from the Persistent folder it goes into a folder
named `.Trash-1000` in the same Persistent folder.

Doing right-click on the Trash icon on the desktop, and choosing "Empty
Trash" does not remove those files. Restarting Tails does not remove
those files either. You have to know where those files are and navigate
to that hidden folder in order to free space on your USB stick.

Without talking about the implementation details, what we could do is:

- Keep this trash on the USB stick, and have it persistent. But still
have it taken into account when doing "Empty Trash".
- Move files out of the persistent volume into the main trash when doing
"Move to trash" on the Persistent folder. So that trash won't be
persistent and will be merged with the main trash. The files are removed
whenever Tails is shut down.
- Automatically empty the trash of the Persistent folder when shutting
down; right before unmounting the persistence volume. I understand that
this will not work when doing an emergency shutdown.

Thoughts?