Implement a quick and dirty version of the Assets#uploadAndConfirmAsset method.

Add 'mime' and 'nodeproxy' as module dependencies
Add _s3upload helper method to perform the actual upload request
Add uploadAndConfirmAsset method that chains the three necessary requests:
    POST /assets (with file metadata)
    PUT <upload_url> (with file body)
    PUT /assets/<file id>/confirm (to confirm the upload)

See #3