[FIX] hr_holidays: add a constraint on interval numbers
[FIX] hr_holidays: add a constraint on interval numbers

Before that commit we could ask for an accrual allocation of 0 hours
every 0 weeks for instance.
As it means nothing to ask for this, we add an sql constraint on these
fields and a default value of 1.

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo