File attachments to xqueue are now done through s3.

No test changes, yet.
Fixed some bugs in s3 upload.  Made code uploads separate from forum image uploads.
Moved external storage settings.  Renamed any variables referencing s3.

Removed Felix's personal info from Github.

Now creates a storage interface only if needs_storage_interface is True.
Added a couple of tests to coderesponse.
Added new aws settings to aws.py (the prod settings).
Minor fix: CapaModule now knows that it requires the storage interface.