Changed AccessControl class to check if an IElement is adminOnly or not instead of by a path (string)
Changed CpkEngine class to accept duplicate entries on the elementsMap (overwrites the existing element by a new one)
Added getters and setters on AbstractElement class  for a new variable that determinates if the element is or not admin only.
Modified the toString method to show the adminOnly variable.
Modified AbstractElementType class to have a new parameter for registrating the elements -> adminOnly (boolean)