Changed word "exhibit" to "exhibition" in heading

For the heading for the list of links to other exhibit pages
containing the item, changed the word "exhibit" to "exhibition"
Test if need "also", and return if no exhibit pages

The code now tests if the word "also" is needed in the heading
to the links to exhibit page(s) - word is not needed if there is not a
link back to the exhibit page that lead the user to the item page.
Also, added a test that just returns if there are no exhibit pages
to link to.