Moved has_course_access from CMS to student.auth (common)
Change has_course_access definition and doc string

- has_course_access renamed to has_course_author_access for clarity
- Changed doc string to clearly state that it determines whether or not
  a user has write access to a course
Merge pull request #6123 from mitocw/bdero/move-course-role-check-to-student

Moved has_course_access from CMS to student.auth (common)
fix export for openassessment drafts (PLAT-249)