Bug 9549: Show local cover images in the OPAC shelf browser

Bug 9549: Show local cover images in the OPAC shelf browser

Add the ability to view local cover images in the shelf browser.

To test:
1. Add a local cover image to a record. Set OPACLocalCoverImages sys pref to "display."
2. Search for the record, go to the Details page, and click on Browse Shelf.
3. Verify that the local cover image appears in the shelf browser.

Sponsored-by: CCSR
Signed-off-by: Melia Meggs <melia@bywatersolutions.com>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>