public void unlockAction()
 {
     if (player.skill_points >= cost)
     {
         Action a = ActionHandlerScript.FindByID(ID);
         a.Unlock();
         btn.interactable     = false;
         player.skill_points -= cost;
         player.UpdateDisplay();
     }
     else
     {
         errorDiplay.text = "Not enough skill points.";
     }
 }