Do not close app on window close with systray icon

[bertwesarg]

[MaartenBaert]

I'm sorry but I disagree with this change. I know some applications do this but I find it really annoying. If a user closes a window, they usually want to close the application, not just hide it. It is not at all obvious that the application will still be running in the background and it will likely lead to users running multiple instances of SSR in parallel without realizing it. Especially since not all desktop environments even have a (visible) system tray.