add user and secret fields.
add s3 field.
add S3 class to model the S3 attribute of the upload object.
add creating status.
Revert "add S3 class to model the S3 attribute of the upload object."

This reverts commit 95cdaa8bf64c4baff0946809a6d72c9822df19ee.
add S3 class to model the upload object's s3 attribute.
add upload field. remove list field.
Merge branch 'df-model'