QPID-4390: Improve the thread safety of java broker management operations

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1459694 13f79535-47bb-0310-9956-ffa450edef68
QPID-4661: Improve broker attribute editing UI to avoid sending of unmodified attributes, improve UI look-&-feel, improve broker attribute changing functionality to avoid unnecessary modifications

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1459695 13f79535-47bb-0310-9956-ffa450edef68