Bug 19826: Add K::Acq::Budget(s) and K::Acq::Fund(s)

Bug 19826: Add K::Acq::Budget(s) and K::Acq::Fund(s)

This patch introduces Koha::Object(s)-derived classes for budgets and funds (aqbudgetperiods and aqbudgets respectively).

C4::Budgets already uses DBIC calls on those tables so transition should be easy on top of this.

To test:
- Check the referenced schema files are the right ones.
- QA scripts shoudl be happy.
- Sign off :-D

Note: the POD coverage report throws a false negative result on singular classes which is trivially wrong.

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>