OEC-375, rake oec:course_evaluations > denormalized course/instructor

The old rake task created courses.csv, instructors.csv plus a mapping file. Now, 'rake oec:course_evaluations' conflates course and instructor data into a single result-set. This relieves the 'secondary' script (owned by Ops) of having to de-normalize the three aforementioned files. Soon, I will remove code associated with 'rake:courses' and 'rake:instructors'.