Motivation for this change

• Various security fixes
• In Thunderbird 52 a new behavior was introduced for replies to mailing list posts: "When replying to a mailing list, reply will be sent to address in From header ignoring Reply-to header". A new preference mail.override_list_reply_to allows to restore the previous behavior.
• Other bug fixes

https://www.mozilla.org/en-US/thunderbird/52.4.0/releasenotes/
https://www.mozilla.org/en-US/security/known-vulnerabilities/thunderbird/#thunderbird52.4 (not updated yet)

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.