This class represents statistical data about another object (Topic, Queue etc). Statistical data
contains the total number of messages and their cumulative size.
Optionally it provides message rates as number of messages per second
and number of bytes per second. Whether or not rate information is available is controlled
by the server configuration. If rate collection is turned off, all rate numbers
are set to 0. However in those cases the application can calculate the rates
based on the absolute numbers taken at periodic intervals.