Create signed URLs in SubmissionFilesController.
Add jQueryFileUpload files.
Add S3_direct_upload gem.
Working on direct uploads to S3.
Fix JS for multiple uploads.
Working uploads + access.
Show uploaded documents.
Remove jQueryFileUpload code. Handle failed uploads.
Keep updated list of uploaded files.
Fix instructor access.
Remove unused include.
S3 progress bars
Merge pull request #596 from UM-USElab/s3

[Reviewed] Direct uploads to S3