enhance chest object handling and save/load functionality

src/de/miaurizius/jgame2d/entity/Entity.java

@@ -95,6 +95,8 @@ public class Entity {
     public boolean stackable;
     public int amt = 1;
     public float lightRadius;
+    public boolean opened;
+    public Entity loot;
 
     public Entity(GamePanel panel) {
         this.panel = panel;
@@ -354,6 +356,7 @@ public class Entity {
         target.speed += knockbackVal;
         target.knockback = true;
     }
+    public void setLoot(Entity loot) {}
 
     // PARTICLE SETUP
     public Color getParticleColor() {