Bug 26933: Improve handling of multiple covers on catalog search results in the OPAC

Bug 26933: Improve handling of multiple covers on catalog search results in the OPAC

This patch implements a book cover slider widget for cover images in
OPAC search results, matching the way we show covers on the detail page.

To test, apply the page and rebuild the OPAC CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

Enable multiple cover image services. The patch was developed with these
services available:

    - Amazon
    - Local cover images
    - Coce (serving up Amazon, Google, and OpenLibrary images)
    - OpenLibrary
    - Baker & Taylor
    - Google
    - Custom cover images (the CustomCoverImages preference)

Perform a variet of searches and confirm that cover images are
displaying correctly, whether there be 0, 1, 2, or more covers
available for each.

Sponsored-by: Athens County Public Libraries
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Laura Escamilla <laura.escamilla@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>