Bug 1633: [SIGNED-OFF] Don't show image tab when inappropriate

Bug 1633: [SIGNED-OFF] Don't show image tab when inappropriate

This patch corrects the bug spotted by Owen Leonard where the Images tab was
showing up even for records that didn't have local cover images attached to
them. The tab is now hidden on the OPAC for records that don't have any
images. In the Intranet, an Images tab will show for staff with permission
to upload images, suggesting that they do so. For staff without that
permission, the tab is not shown.

This permission also disables returning images via the opac-image.pl and
catalogue/image.pl scripts when local cover images have been disabled.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Signed-off-by: Koustubha Kale <kmkale@anantcorp.com>