Schoology fixes

[mgwozdz-unicon]

• Handle array audience
• Use nrps accept type
• Note that score comment must be non-null

It is also noteworthy that while AGS works fully from an API perspective, Schoology requires each assignment to have a "Category" associated with it in order for the assignment to be visible in the gradebook UI. Pearson documented their workaround here, instructing teachers on how to add the category manually for each assignment: https://help.pearsoncmg.com/integration/cg/instructor/content/get_started-schoology-13.htm

[mgwozdz-unicon]

I confirmed that this code still works with both Canvas and D2L.