S3 oversized messages

Add S3 support to queuel for oversized messages. 

URLs
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- [Pivotal Epic #1128518](https://www.pivotaltracker.com/epic/show/1128518)

Notes
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`bucket_name`, `access_key` and `secret_access_key` need to be supplied to the credentials hash to use S3. See `config/s3_example.yml`