datalib: Introducing get_courses_wmanagers() for print_courses() usage

datalib: Introducing get_courses_wmanagers() for print_courses() usage

For an efficient print_courses() we need to grab in a constant number
of queries...

 - course data
 - "course manager" role assignments
 - user records for the coursemanagers' fullname()

So here we do it in 2 DB queries. The 2nd one (grabbing RAs and user
records) can be expensive if we are dealing with a large number of
courses.

Which we shouldn't - When the number of courses is large the course
listing doesn't come this way anyway...