SyncSettingsReborn v4.1.0

This release adds PackageSync-style sync capabilities alongside the existing
GitHub Gist backend.

New commands

- SyncSettingsReborn: Backup to Zip — offline, portable backup of your
  Packages/User folder (your `access_token` is never included).
- SyncSettingsReborn: Backup Package List — back up only the installed
  package list (`Package Control.sublime-settings`).
- SyncSettingsReborn: Restore from Zip — restore from a previously created zip.
- SyncSettingsReborn: Sync Online — Define Folder / Push / Pull: a Dropbox /
  Google Drive / OneDrive based workflow without any background process.

New settings

- `prompt_for_location` / `backup_path` — choose where backups are read/written.
- `preserve_packages` (default true) — on restore, the incoming
  `installed_packages` is merged with the local list instead of overwriting it,
  so packages only on this machine are kept.
- `ignore_dirs` — skip entire directories when collecting files.
- `online_sync_folder` — folder used by the Sync Online commands.

Note: the GitHub Gist backend remains the default zero-config option; the new
Zip / Online commands are additional ways to sync, not a replacement.
