CLC-4321 - Added #official_sections method to CanvasCourseGradeExportController, for use with front-end to choose appropriate export section
CLC-4321 - Updated #official_section_identifiers to cache result in instance var. Added #grade_types_present for validation of grade data present in frontend. Updated #official_sections to include formatted display name. Added #section_terms to detect more than one term present for course site.
CLC-4321 - Converted CanvasCourseGradeExportController#official_sections into #export_options, now serving grade types available, as well as sections terms present
CLC-4321 - Migrated Course Grade Export authorization check request to factory
CLC-4321 - Finished Canvas::Egrades#official_student_grades
CLC-4321 - Added #official_student_grades_csv to Canvas::Egrades
CLC-4321 - Finished #download_egrades_csv in CanvasCourseGradeExportController
CLC-4321 - Added logic to AngularJS front-end for Canvas Course Grade Export for handling export state validation