CLC-4321 - Modified Canvas course users fixture for inclusion of number and letter grades
CLC-4321 - Removed Canvas::CourseUsers#course_grades_csv
CLC-4321 - Added Canvas::Egrades model to provide data related to eGrades export
CLC-4321 - Added #export_options method to CanvasCourseGradeExportController, for use with front-end to validate export state and provide section selector.
Refactored #download_egrades_csv to use Canvas::Egrades#official_student_grades_csv for CSV download.
CLC-4321 - Migrated Course Grade Export authorization check request to factory
Added validation logic with errors in front-end.
CLC-4321 - Appeasing the Javascript Gods
CLC-4321 - Applied .cc-button class, added .cc-page-course-grade-export-download-button class for extra padding
CLC-4321 - Added and removed unnecessary newlines
CLC-4321 - Added required parameters to GET request for #download_egrades_csv
CLC-4321 - Added notice to contact support for Authorization check failure
CLC-4321 - Revised letter grade error in eGrades export as per CANVAS-480
CLC-4321 - Fixed Rspec tests to properly match true and false values
Merge pull request #3093 from redconfetti/QA-CLC-4321-egrades-export

[QA] CLC-4321 - Investigate possible issues with pending eGrades Export tool