1) Simplify gallery_rest to return flat models, no children and do no
validation for now.
2) Flatten the REST replies and use HTTP codes to indicate
success/failure instead of additional status messages.
3) Use the message and error code support in the base Exception class,
instead of brewing our own in Rest_Exception.
4) Get rid of rest::success() and rest::fail() -- we only need
rest::reply() since all failures are covered by throwing an
exception.
5) Get rid of /rest/access_key and just use /rest for authentication.
6) Inline and simplify rest::normalize_request since we only use it once
7) Change rest::set_active_user to succeed or throw an exception
8) Extract Rest_Exception::sendHeaders into rest::send_headers()
Here's what's currently broken:
1) Data validation. There currently is none
2) Logging. That's gone too
3) image block and tag code is broken
4) Tests are broken
5) No movie support
