Return 403 on unauthorized upload when over account quota

If you try an unauthorized upload into a container that is over quota you get
a 403 instead of a 413, but if you try to unauthorized upload when an
*account* is over quota you can see the 413 even though the upload would have
been rejected by the authorize callback.  By wrapping the authorize callback
associated with the incoming request we can make sure to only return our 413
when the request would have been authorized otherwise.

Drive by doc fixes thanks to acoles:

 * State that container_quotas should be after auth middleware in
   the class doc string.
 * Add note to proxy-server.conf.sample that account_quotas should
   be after auth middleware.

The equivalent statements are already in place for each quota
middleware.

Doc-Impact

Closes-Bug: #1387415
Change-Id: I2a88b3ec79d35bfdd73ea6ad64e376b7c7af4ea6