Last life cycle refactor updates + add comprehensive documentation (#57)

Co-authored-by: Michal Pikulski <michal.a.pikulski@gmail.com>
Reviewed-on: #57

Assets/Scripts/PuzzleS/ObjectiveStepBehaviour.cs

@@ -83,10 +83,8 @@ namespace PuzzleS
             }
         }
         
-        protected override void OnDestroy()
+        internal override void OnManagedDestroy()
         {
-            base.OnDestroy();
-            
             if (PuzzleManager.Instance != null && stepData != null)
             {
                 PuzzleManager.Instance.UnregisterStepBehaviour(this);