Add support for z-index parameters in Entity which determines the Entity rendering order

api/src/main/java/com/bartlomiejpluta/base/api/entity/Entity.java

@@ -31,4 +31,8 @@ public interface Entity extends Movable, Renderable, Updatable {
    void setBlocking(boolean blocking);
 
    void changeEntitySet(String entitySetUid);
+
+   int getZIndex();
+
+   void setZIndex(int zIndex);
 }

api/src/main/java/com/bartlomiejpluta/base/lib/entity/EntityDelegate.java

@@ -219,6 +219,16 @@ public abstract class EntityDelegate implements Entity {
       entity.changeEntitySet(entitySetUid);
    }
 
+   @Override
+   public int getZIndex() {
+      return entity.getZIndex();
+   }
+
+   @Override
+   public void setZIndex(int zIndex) {
+      entity.setZIndex(zIndex);
+   }
+
    @Override
    public void update(float dt) {
       entity.update(dt);