Updates and fixes for the social stream API.

- Social stream photo updates should use the new photo storage
  system instead of storing the image content in BLOBs.
- Package names need to be text, not numbers.  The status update
  documentation was incorrect.
- Social stream photos will include a URI the caller can open to
  get the photo content.
- Removed the max photo bytes from the stream item limit query,
  as we'll do appropriate resizing with the photo storage system.

Change-Id: I103ee1340c1a3772ae37add3684b0658c241a49c