Add "item in context" information

This will be needed for the ingest into Fedora. Basically, we want the link to
an exhibition page that contains the item. Note that there are pseudo-exhibits,
such as the Omeka Demo exhibit, which may contain an item. So we check to make
sure that the exhibit name matches the Omeka collection name for the item.
Also, we just need one "item in context" value, so we just use the first valid
one we get.
This commit contains debugging code which needs to be removed.
Handle case where item is not in any exhibition

The code now handles the case where the item is not in an exhibition.
Before the fix, would get an error and the xml would not display.
NOTE that the debug code is still there, and still needs to be
removed.
Call CulCustomizePlugin::return_exhibit_pages_containing_current_item with argument

CulCustomizePlugin::return_exhibit_pages_containing_current_item now takes an argument
(commit 79e34fc0b51a5025888f5686c2a17260f9cb523d in CulCustomize)
This argument was needed to have the item-in-context functionality work in the
collection context - get_current_record('item') was not working, probably because
the current record is a collection. So cul-omeka-output was not working when used
in the Browse Items screen for a collection.
Remove debug code from _buildItemInContext