Bug 32402: Add "Modification date" to OPAC Lists table

Bug 32402: Add "Modification date" to OPAC Lists table

This change adds a "Modification date" column to the
OPAC Lists table, so that you can see when a list was last modified.

Test plan:
1. Apply patch
2. Create a public list and a private list
3. Go to http://localhost:8080/cgi-bin/koha/opac-shelves.pl?op=list&public=1
4. Note that "Modification date" appears in the relevant date format
on both the "Your lists" and "Public lists" tabs

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>