Backport Time Sync changes to WUTS

[dkosmari]

Summary of changes:

• Use libwupsxx as an external submodule; code as been updated for the current libwupsxx, as some of the wups::config::item API changed.
• Sources have a full copyright notice (year and author).
• New option: synchronize when closing config (if changes were made). Closing the menu does not synchronize the clock unless this option is enabled (and any config was changed).
• "Syncing Enabled" option was renamed to "Synchronize On Boot". Old config option will be migrated to the new one (sync -> sync_on_boot).
• There's now an option to explicitly run the synchronization task inside the config menu.
• Synchronization thread can now be safely canceled.
• timezone_* classes and files were renamed to time_zone_*.
• Plugin description, license and authors were removed from the Makefile. They're only used in main.cpp, there's no point in creating global macros for them.

I left the README unchanged, as you'll probably want to adjust names, phrasing, etc.

[Nightkingale]

This all looks good to me! Thank you, as per usual!