Added default SceneType for SceneManager

This is used as the initial scene that is loaded when the SceneManager
is created.

src/main/java/org/hirw/game/SceneManager.java

@@ -5,6 +5,8 @@ import java.util.Map;
 import lombok.Getter;
 
 final class SceneManager {
+  private static final SceneType DEFAULT_SCENE_TYPE = SceneType.SPLASH;
+
   private static final EnumMap<SceneType, Scene> SCENES =
       new EnumMap<>(
           Map.of(
@@ -12,7 +14,7 @@ final class SceneManager {
               SceneType.MENU, new SplashScene(),
               SceneType.GAME, new SplashScene()));
 
-  @Getter private static Scene scene = SCENES.get(SceneType.SPLASH);
+  @Getter private static Scene scene = SCENES.get(DEFAULT_SCENE_TYPE);
 
   public static void setScene(SceneType sType) {
     scene = SCENES.get(sType);