Add SpaceStars background scene

[kwreen]

Closes https://github.com/KKMMMTTT/AstroSoar/issues/4

The game world involves moving in space. The background should be of the universe where stars are present in the distance.

With the following Scene configuration..

public class TbdScene : Scene
    {
        private readonly SpaceStars spaceStars;
        public TbdScene()
        {
            TextureImage image = new TextureImage("star.png", 900, 900);
            spaceStars = new SpaceStars(image, 1000, 1000, 125);
        }
        public override void Draw(ICanvas canvas)
        {
            spaceStars.Draw(canvas);
        }
    }

..we can obtain this example of generated space stars

Notes

• Fetched a random star image from Google to use as a representation for the stars but we will need to replace this with an asset from the Art team. cc @KKMMMTTT/art