QPID-5984: [Java Broker] Queue tab improvements

* Revert to two column layout to optimise use of screen space
* Expose flow control, oldest message age and maximum delivery attempt attributes

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1617160 13f79535-47bb-0310-9956-ffa450edef68