Bug 12529: Add a syspref to make overdue notices respect holidays

Bug 12529: Add a syspref to make overdue notices respect holidays

Test Plan

Set up some overdue triggers, for example 5,10,15
Set up some holidays
Create some items that are past due (one due 5 days, 10 days ago etc)
Run the overdue notices script (misc/cronjobs/overdue_notices.pl)

Notice holidays are ignored

Apply the patch,
Switch the OverdueNoticeCalendar syspref to Use calendar

Run the overdue notices again
Notice holidays are now taken into account

Sponsored-by: BSZ
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>