[Direct Edit] Do not use the account download folder

Direct Edit download folder is always set to "$HOME/.nuxeo-drive/edit" (on C: usually).
This may be problematic when the download folder is on another partition:

• the blob is downloaded into the account download folder (let's say "d:/.tmp")
• then the file is moved from D: to C:

There may be complications and useless copies.

Instead, when downloading the blob, we should use a custom download folder and not relying on the account's one.