CLC-4072 Make class calendar table indexes unique
Merge pull request #2811 from ctweney/clc-4072

CLC-4072 Make class calendar table indexes unique
CLC-4091 - Added 'latest_term_enrollment_csv_set' timestamp attribute to Canvas::Synchronization model
CLC-4091 - Added comments to Canvas::SiteMembershipsMaintainer concerning dependency on Canvas::TermEnrollmentsCsv
CLC-4091 - Added rake task for exporting Canvas enrollments to CSV set
CLC-4091 - Added #delete_files_if_exists helper to Rspec environment for clearing temporary files
CLC-4091 - Moved #csv_count method from Canvas::RefreshAllCampusData to parent class Canvas::Csv, for use by all subclasses
CLC-4091 - Added Canvas::TermEnrollmentsCsv to export and provide section enrollments from CSV files sets
CLC-4091 - Converted last argument of Canvas::SiteMembershipsMaintainer initializer to options hash