Improvements to email options

Please consider adding more options for who you can target with emails re. activities/courses.

I have no way of setting up a recurring email to only be sent to people overdue on their learning.
This means I end up using the 'Not Attempted' 'Incomplete' filters instead but then I'm chasing people who are not always past their due date yet.

The other choice I have is to set up a ton of individual emails to go out at set points after the due date which is time consuming to set up for every course.