Ensure the off-week timesheet is created 

When someone logs in or is reminded to login for the invoice-week 
timesheet, ensure the previous-week timesheet is generated first.

Doing this because I'm seeing a lot of confusing data where the off-week
timesheet is simply never created.
blow up on failure
Revert "blow up on failure"

This reverts commit 3e204b62e565a28c233477fb3710bbd87b2ded19.
when a user marks timesheet ready, marks last week

Up to now when someone marked a timesheet ready to invoice, they did not
actually save the previous week timesheet as ready to invoice, which is
problematic
Made the validation more accurate

This should only validate for invoice weeks