Bug 22032: Improve local cover image tab on detail page

Bug 22032: Improve local cover image tab on detail page

This patch makes a variety of improvements to the images tab of the
staff client's bibliographic detail page.

To test, apply the patch and regenerate the staff client CSS.

 - Enable the LocalCoverImages system preference.
 - Locate a bibliographic record which has no images attached.
   - There should be a "no images" message and an upload button.
     - Upload an image and return to the detail page.
       - The "Images" tab should have a nicely-styled thumbnail of the
         image you uploaded.
         - Test the "Delete image" link: It should ask for a
           confirmation. If you confirm, the image should disappear and
           a "loading" spinner should appear.
           - When the image has been deleted the thumbnail container
             should disappear and the "no images" message should
             reappear.
 - Test this process with AllowMultipleCovers enabled and disabled.

Extra credit: Modify the AJAX url in the removeLocalImage
function in detail.tt. After misspelling a parameter name or the URL
path, clicking the "Delete image" link should trigger an alert and
re-show the image thumbnail.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>