Bug 10320 - Integrate OverDrive search into OPAC

Bug 10320 - Integrate OverDrive search into OPAC

Show any relevant results from the OverDrive ebook/audiobook service
on the OPAC search. This is done by showing a link with "Found xx
results in the library's OverDrive collection" at the top of search
results and linking to a page that shows the full results.

This requires an OverDrive developer account, and is enabled by
setting the OverDriveClientKey and OverDriveClientSecret
system preferences.  In addition, this patch adds the
OverDriveLibraryID system preference.

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Henry Bankhead <hbankhead@losgatosca.gov>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>