Make the loading screen used more

[hhyyrylainen]

A loading screen should be made, that at least would show while auto-evo is running.
I read that Godot 4.0 adds support for background loading stuff, so that makes it more possible to make a loading screen.

[hhyyrylainen]

So now there is a kind of a loading screen, but it is only used for one thing (waiting for auto-evo).

[hhyyrylainen]

This is still relevant, our asset loading just lags the game (well due to #1804 not being done this happens when starting the game executable), and doesn't show the loading screen. I think we may need to wait for Godot 4.0, though to make this...