Timesheet reminders and draft client invoices

The Timesheet reminders job emails a contractor whose timesheet for a finished week is missing or still a draft, once per week. The Draft client invoices job gathers approved, unbilled time into one draft invoice per client.

• At the notify level (the default) the job only says which invoices are ready to raise; at approve it asks for approval first; at act it drafts them.
• An invoice is only ever drafted. Posting it to receivables stays a person's act.
• A client that needs its purchase order number on the invoice is left for a person to raise.