Rename "Tor Browser" shortcuts and folders as "Downloads"

Design

• “Downloads” → “~/Downloads”, for the amnesiac version
• “Downloads (persistent)” → “~/Persistent/Downloads”, for the persistent version
  • Migration: #15028 (comment 29539)

Implementation

• Old feature branch: wip/feature/15028-rename-tor-browser
• This requires disabling at least part of the GNOME localization code for xdg-user-dirs: ~/Downloads MUST NOT be renamed to a localized version anymore.

User research findings

• During usability tests, participants have a very hard time knowing how to save something from Tor Browser. #10422 would be an ideal solution, but having better named folders would really help meanwhile.

• During a Tails training, users were asked to open Tor Browser, after already having a few Nautilus windows open. They clicked on the “Tor Browser” directory on the side panel in the open Nautilus window but were not sure what to do next since that just brought them to an empty directory.

  Because 100% of these participants being trained had never used any Linux desktop before, they had no baseline expectations of how similar/dissimilar the Tails desktop would be to the Windows, OS X, iOS or Android interfaces they are also only somewhat used to.

• During #18762 (closed), P1 thought that "Places → Tor Browser" opened Tor Browser.