Made SheetBuilder rely on global settings rather than global renderer.

Additionally exposed an InitializeSettings method on game to initialize the global settings so that other classes can set up all the secret dependencies on the global settings required.

OpenRA.Lint/YamlChecker.cs

@@ -55,9 +55,7 @@ namespace OpenRA.Lint
 				FieldLoader.UnknownFieldAction = (s, f) => EmitError("FieldLoader: Missing field `{0}` on `{1}`".F(s, f.Name));
 
 				AppDomain.CurrentDomain.AssemblyResolve += GlobalFileSystem.ResolveAssembly;
-				Game.Renderer = new Graphics.Renderer(
-					new GraphicSettings() { Renderer = "Null", NumTempBuffers = 0, SheetSize = 0 },
-					new ServerSettings());
+				Game.InitializeSettings(Arguments.Empty);
 				Game.modData = new ModData(mod);
 
 				IEnumerable<Map> maps;