7.0 worked days from timesheet payslip run integration

This PR adds the possibility in payslip batch to import worked days from timesheet. This adds a simple box to check in the wizard form if the user wants to use this functionnality.

Also, I moved the yml test to python unittest. The reason for this is that unittest is allows to create data with loops, which does not seem to work in yml. This makes the tests easier to read and understand.

For the method get_timesheets_from_employee, it is a former section of the method import_worked_days that I separated so that it could be called by the payslip run wizard (hr_payslip_employees).
Please use present imperative ("Add a button") if you don't use "This module" as a subject