Bug 27325: Fix singular/plural forms on the OPAC dashboard

Bug 27325: Fix singular/plural forms on the OPAC dashboard

This patch adds handling of plurals to the display of counts on the
logged-in user's dashboard: checkouts, overdues, etc.

To test, apply the patch and log in to the OPAC.

 - Go to the OPAC main page and check the user dashboard area.
 - Confirm that the correct numbers and plural forms are shown for
   checkouts, overdues, holds pending, holds waiting, and messages.
 - Test each of those categories with counts of 0, 1, and more than one
   to confirm that the plural forms are correct.
 - Test with various counts of each type of message: OPAC notes as
   defined when editing a patron record and notes added via the checkout
   page.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>