Integrate Marconi Client with Swift

The idea is to put a blob on swift (make pluggable so you can target glusterfs, nas, gridfs, ceph, etc.) and then just reference it from the message, rather than embedding it.

A message object would have the usual TTL and body attributes, but maybe also a "blob" or something. The client would under the covers PUT it to a swift container, and insert a link into the message's body document. On the other end, the receiver would then download the blob and "put that thing back where it came from". It could generate a temp URI or something, and have the object auto-expire