Adding new step definition for links that are loaded but not visually visible

New step definition for checking for links that are loaded on the page, but not visually visible. In my case I needed to check the second level menu items in a drop-down menu were loaded but hidden.

I've stuck with the naming convention of similar methods here, an alternative would be to name this "Then the :link link is loaded but not visually visible" which might be more easily understandable.