Add support for scheduling by weeks and week working days

[IvanBond]

Current version supports schedule by "each X days", "Month + calendar/working days of month", but no support for "weekly" scenarios.
E.g. "each first working day of week" or "end of each last working day of week".
Or, "each 1st day of week 10, week 20, week 30" - e.g. during certain project.