Bug 13949 - Item search should have holding library

Bug 13949 - Item search should have holding library

This patch adds holding library ("current location") to the list of
fields available in the item search form.

To test, apply the patch and go to Search -> Item search.

- Perform a search using the "current location" option and verify that
  it returns the correct results.
- Try other searches to confirm that they work as before.

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>