Improve visibility of mouse director indicator

[Stehsaer]

Default indicator is colored red, but in actual play the indicator's visibility is not so good. Some improvements are requested. Potential improvements may be:

1. add a white outline to the indicator
2. use a black bar with white outline or white bar with black outline as the indicator
3. make it configurable, can be set through dragging images into mod folder and editing the .cfg files

[Stehsaer]

what's more, instead of bar, using a cross may be even better. for this reason I strongly recommend adding a customizable indicator image setting.

[Stehsaer]

AtmosphereAutopilot/AtmosphereAutopilot/Modules/MouseDirector.cs

Lines 119 to 145 in 9e4323c

	public class CenterIndicator : MonoBehaviour
	{
	Material mat = new Material(Shader.Find("Sprites/Default"));
	Vector3 startVector = new Vector3(0.494f, 0.5f, -0.001f);
	Vector3 endVector = new Vector3(0.506f, 0.5f, -0.001f);
	//public new bool enabled = false;
	public void OnPostRender()
	{
	if (enabled)
	{
	GL.PushMatrix();
	mat.SetPass(0);
	mat.color = Color.red;
	GL.LoadOrtho();
	GL.Begin(GL.LINES);
	GL.Color(Color.red);
	GL.Vertex(startVector);
	GL.Vertex(endVector);
	GL.End();
	GL.PopMatrix();
	enabled = false;
	}
	}
	}

It's here that should be modified.