Add ability to upload directly to S3 from the scoreboard

[rbclark]

We currently have to manually upload to S3 and then post the link on the scoreboard. It would be easier if we could just upload the file directly on the scoreboard and then have it include a link to the challenge. Also we can have the scoreboard automatically change the permissions on the file when the challenge actually opens which means people won't be able to find the challenges ahead of time.