Implement Trash directory

Intended behavior:

- [x] The Trash directory should show all files with `trashed = true` on Drive.
- [x] Removing a file (`unlink`) from any directory mark it as trashed.
- [x] Moving a file (`rename`) from any directory to Trash should mark it as trashed (f273d25).
- [x] Removing a file (`unlink`) from Trash should delete it permanently (bd528c31d8253d9c28d24bf3817f76f864790e23, 11ebeb65443c1516a0e1f31275906cd47e83d130)
- [ ] Moving a file (`rename`) from Trash to anywhere else should mark the file as not trashed and possibly update its parent.
- [ ] Recursively removing a directory (`rm -r`) should preserve the hierarchy of its content even when moved to Trash