Godot 4 port

[vmedea]

This is a start of a port to Godot 4. It makes the changes to port the main application to Godot 4. Some notes:

• Disables GIF export for now. This will require porting the stuff under addons/gdgifexporter. (fixed, thanks to @isirode)

• The color selector is a lot larger in Godot 4. I haven't found a nice solution for this.

• The background stars particle system isn't correct. (i think this is fixed now)

[isirode]

Nice work for the port of the shaders.

I've made you a pull request (GIF, web support, Godot 4.1) vmedea, for information.