[SE-4175] Add CCX ID to generated filename prefixes
This pull requests adds a new feature to include CCX course IDs in the generated course filenames used for downloading reports, etc.
The suffix appended to the generated filename prefix is following the `<separator>ccx<ccx id>` pattern, to ensure unique filename generation per ccx - previously all CCX courses were downloaded with the same name.
![Screenshot 2021-03-16 at 16 22 12](https://user-images.githubusercontent.com/19173947/111349994-f1c42980-8681-11eb-8fff-d28024899957.png)
*Sandbox URL*: Due to an `DeprecatedEdxPlatformImportError` exception the sandbox is not provisioned.
*Merge deadline*: None
1. Enable `ALLOW_COURSE_STAFF_GRADE_DOWNLOADS`, `ENABLE_GRADE_DOWNLOADS`, and `ENABLE_COURSE_FILENAME_CCX_SUFFIX` features.
2. Create a course
3. Enable CCX for the course in the advanced settings
4. Create a new CCX for the course
5. Generate and download grades
*Author notes and concerns*:
[ ] @mavidser
[ ] TBD
I believe this is with the arch team, can someone please review?