made changes in Order generated sales csv in Instructor Dashboard.
 The total_registration_codes and total_used_codes
  were not correctly stored in the csv file.

1) The total_registration_codes were not filtered with
 course_id.
2) The total_used_codes that a user had redeemed
 were not correctly included in the CSV.

added a fix in the courseware view to let the users visit the courseware if they have enrolled in the course by clicking on the enrollment link
Merge pull request #5452 from edx/muhhshoaib/fix-issues-in-financial-download-csv-and-courseware-views

Fixed Issues related to order generated sales csv and course ware access