Bug 28488: Javascript error in self-checkout (__ is not defined)

Bug 28488: Javascript error in self-checkout (__ is not defined)

This patch adds inclusion of the internationalization JavaScript which
is required by the newest version of the DataTables include. It
references the double-underscore function provided by i18n.js.

To test, apply the patch and log into the self-checkout system as a user
with checkouts. The table of checkouts should display correctly and
there should be no JavaScript errors in the console.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>