Implement health modification on enemy kill; add HealOnKillModifier and update death behavior

Assets/Scripts/Interfaces/IDeathBehavior.cs

@@ -1,7 +1,10 @@
+using JetBrains.Annotations;
+using UnityEngine;
+
 namespace Interfaces
 {
     public interface IDeathBehavior
     {
-        void Die();
+        void Die([CanBeNull] GameObject killer = null);
     }
 }