Bug 18736: (follow-up) Fix missing rounding and bad formatting

Bug 18736: (follow-up) Fix missing rounding and bad formatting

This patch:
Adds a missing use
Uses 'Koha::Number::Price->round()' instead of 'format()' to ensure numeric
returns
Ensures too big numbers don't crash round()
Uses syspref in 'GetBudgetHierarchy'

To test:
Follow previous test plan
Check values on admin/aqbudgets.pl are affected by syspref
Ensure values throughout acquisitions are correctly calculated/displayed
(even when greater than 1,000)

Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>