A ClientManifest is a data object containing information about a client
on the server, including attributes, a list of the rooms the client is
in, and a list of rooms the client is observing. ClientManifest objects
are used by the RoomSnapshot class to represent the clients in its occupant
and observer lists.
An AttributeCollection containing the persistent attributes
stored by this client's user account. Applies to client manifests
representing clients that are logged into a user account only.