GTK4 Port

Some stuff left to do:

• Needs more testing
• I have no idea how to fix the Snap package CI build (the image lacks gtk4 package)
• Save dialog still has regressions (compression settings)
• Needs general git history and code cleanup
• Some minor translation fixes
  • Auth dialog should not have : on the end of username and password labels
  • Compression setting label should not have : on the end

closes: #316 (closed)