Request: start with overlay disabled

[ArmEagle]

I'd like to be able to start the program with the overlay not showing.

Would be fine if this was just a Command Line Argument.

(Together with my other request - window position - this would make my flow, starting for Elite Dangerous, just perfect.)

[Hotrian]

Should be easy enough. I'm currently attempting to migrate to Unity 2019.x, but I should be able to push this into the next build.