Increase the maximum number of page result sets to 24
Increase the maximum number of page result sets to 24

Increase the maximum number of fetched page result sets from 4 to 24
when getting an instructor's course enrollments. Otherwise, instructors
with a large number of course enrollments cannot see their most recent
courses.

At the moment, 5 pages is actually sufficient. But, there's no real
harm in setting this higher. The limit was originally set to avoid
runaway loops.

Resolves #12.

ucalgary/d2l-grades-export,ucalgary/d2l-grades-export