Allow automatic importing of flags and points with `/challenge fromcsv`

[KNOXDEV]

[KNOXDEV]

Possibly tackling attachments as well?

[KNOXDEV]

Thinking about it further, I think bulk importing from CSV is tricky due to how nested the data structure is.

I think a better approach would be to import from JSON. That way, we might eventually be able to reuse the behavior for cough cough other types of APIs.

That would naturally accomplish the original point of this issue as well.