Offer user quick restart if settings change

Ever been annoyed by those settings in the menu that require a restart? Well I haven't fixed those. But I have added a little dialog to save you some time! That's almost as good right?

![Restart Now?](http://imgur.com/HQJr5fT.png)

Hit the button and the game will be loading again within a second or two.

Doesn't check for mouse-lock in anticipation of #5597 landing.


> I'd prefer to not dig too deep in the language bag-of-tricks and express these as Game.Exit(ExitKind.Normal) or Game.Exit(ExitKind.Restart) rather than using optional args. I don't think that's too verbose.

:+1:.  The `RunStatus` enum could be used for this.