BREAKING CHANGE: For GNOME DE users, closing window will terminate process completely. For other DE users clicking on close button will hide the window to tray (the same as before). This behaviour is controlled by two options: "Hide window to tray instead of closing it" and "Minimize window to tray instead of app bar". This change is aimed to bring consistent behaviour with the rest of the ecosystem in GNOME environment, where tray widget is not available by default (issue #82).