SSP-2573, SSP-2571 Better Off Plan email targeting

Now every coach and/or owner gets at most one email from the bulk
On/Off Plan status calculation job and it only lists students
with whom they have some sort of relationship... either as a coach
or as an owner of the student's active, off-plan plan.

Also happens to address the problem of sorting student names in these
emails. They're now sorted by last name, then first name.