BUG 11602: [ENH] Fix localcover display

BUG 11602: [ENH] Fix localcover display

Adds a css class of thumbnail to local covers.
Don't show the 1px "No image found" image
(since we'll ususally try another image provider)

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Box with "No cover image availabe" fixed when syspref OPACLocalCoverImages
set to display

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
(cherry picked from commit a06793dc584212dde20f985740691b7e49074c76)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>