Payroll related document classes (AnnotationLine, PaySheetLine, PaySheetTransactionLine, PaySheetCell) are not different from Invoice-related classes.

This work aims to remove these document classes and base the portal types on the generic invoice classes.

This work started after finding out that Pay Sheet Lines were appearing in the "Account Statement" report, on side of Pay Sheet Transaction Lines. This happened as PaySheetLines is overiding the "isAccountable" method to return True. This merge request, besides removing duplicate code, fixes the accountable property of Pay Sheet Lines, and updates the call to the inventory API to generate correct accounting/payroll reports.