Add title to link back to exhibit page

Code now iterates thru the exhibit pages that contain the item,
and checks that $_SERVER['HTTP_REFERER'] points to one of these
pages. If so, the link will print, using as text the title of
the exhibit page. Also, since this is a "legacy" theme that
mimics the behavior of Omeka 1.5.3, where there were sections
with no landing page, we also compare with the first child
Intermediate commit: Contains code for legacy themes

This intermediate commit contains the code to handle the legacy
themes and the behavior mimicking the Omeka 1.5.3 sections.
This code will be moved to the CulCustomize plugin in a future
commit (probably the next commit)
Modified code for link back to exhibit page in item page

Moved most of the orginal functionality added in a previous commit
from item.php into the CulCustomize plugin, since this
functionality is needed in all the themes.
Also, now the link to the exhibit page displays the page title
(including parent pages). Also, now the links to other pages
containing the item also display on top of the page, and the list
does not repeat the aforementioned link back to the exhibit page.
Modified a few comments
Removed commented-out line of code