Squashed commits:
[26bd4e74] US Payslip
[1a1ef897] PA Pennsylvania
[ece62752] HI Hawaii
[f2fd9980] [FIX] l10n_us_hr_payroll: Virginia 2021 test had 2020 dates
[cc9f76f8] WA Washington
[24835fc1] PA Pennsylvania
[fe3cd269] IA Iowa
[6f034b07] DE Delaware
[2e6835e0] AL Alabama
[70a2caa1] [FIX] l10n_us_hr_payroll: Removed Debug From Maine Test
There is a distinct difference between the way payslips compute categories and how they sum categories over periods of time.
On payslips, children of categories are included, however not if using `sum_category` over a period of time.
After this commit they behave the same by recursively computing child categories in the `sum_category` query.
In stock Odoo, summing anything in payroll rules (but most importantly rule amounts and category amounts by code), the considered payslips are referenced from their `date_from` field. However in the USA, it is in fact the `date_to` that is more important (or accounting date). A Payslip made for 2019-12-20 to 2020-01-04 should in fact be considered a '2020' payslip, and thus the summation on other '2020' payslips must find it by considering payslips `date_to`.
