Bug 27550: "Duplicate budget" does not keep users associated with that budget

Bug 27550: "Duplicate budget" does not keep users associated with that budget

When a budget is duplicated, Owner is copied but not Users

Test plan :
Home > Administration > Budgets
1)Create a budget to allow (active or inactive)
2)Give it some funds by filling up the form, especially Owner and
User(s)
3)Submit then go back to the Budgets dashboard
4)Duplicate the Budget and click on its name
5)Edit it and notice that User(s) is empty
6)Apply the patch
7)Repeat from 1) to 5)

Signed-off-by: Samu Heiskanen <samu.heiskanen@hypernova.fi>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>