Move ModContent out of the engine.

OpenRA.Mods.Common/LoadScreens/ModChooserLoadScreen.cs

@@ -11,7 +11,6 @@
 
 using System.Collections.Generic;
 using System.Drawing;
-using System.IO;
 using OpenRA.Graphics;
 using OpenRA.Widgets;
 
@@ -58,5 +57,10 @@ namespace OpenRA.Mods.Common.LoadScreens
 			if (sprite != null)
 				sprite.Sheet.Dispose();
 		}
+
+		public bool RequiredContentIsInstalled()
+		{
+			return true;
+		}
 	}
 }