QPID-5496: WIP on a common way of configuring the default-group for a queue, and allowing queues with 'shared groups' to support non-grouped messages

git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/QPID-5496_default_groups@1559833 13f79535-47bb-0310-9956-ffa450edef68