attachments should be stored in the course directory

[cg2v]

There seems to be no good reason for attachments to live in a single toplevel directory. Why aren't they in the course or assessment directory?

[TheodorJ]

Wow, apparently all of the attachments for all courses seem to be stored in the ./attachments folder with no heirarchy. Leaving this one open.

[victorhuangwq]

Not sure if this issue is still relevant in the latest master. Let me know if it is.

[mtoupsUNO]

I'm pretty sure it still is relevant. I still observe this behavior in my deployment. I'm not running the latest master there, but it isn't very out of date. And I see no meaningful changes to app/models/attachment.rb in the past two years.

[victorhuangwq]

@mtoupsUNO thank you for the update. I will keep this open.

[damianhxy]

Addressed in #1810 (currently in develop) by switching to ActiveStorage.