Bug 28179: Add the Chocolat gallery lightbox JS library

Bug 28179: Add the Chocolat gallery lightbox JS library

Chocolat is a lightbox JS library.
https://chocolat.insipi.de
https://github.com/nicolas-t/Chocolat
https://chocolat.gitbook.io

Why Chocolat? It's released under the GPL v3 license, easy to use,
configure and extend, and is still maintained/active.

(and it has a nice name)

Sponsored-by: Gerhard Sondermann Dialog e.K. (presseplus.de, presseshop.at, presseshop.ch)
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Rasmus Leißner <rasmus.leissner@solutions-factory.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>