Bug 36081: Use multivalue_preference

Bug 36081: Use multivalue_preference

C4::Context->multivalue_preference is not used so far and split on |
However the values of "multiple" sysprefs are separated by... comma!

Let support both here.

This patch also removes silly JS code in the template.

Signed-off-by: Magnus Enger <magnus@libriotech.no>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>