INT-2823 Add QueueChannelOperations

Operations on QueueChannel (clear, getQueueSize etc) are not available
when the IntegrationMBeanExporter is configured because they
are not declared on the PollableChannel interface.

Add an additional interface QueueChannelOperations.

The proxy proxies all interfaces so users can cast the
proxy to QueueChannelOperations to use its methods.
Merge pull request #732 from garyrussell/INT-2823

* garyrussell-INT-2823:
  INT-2823 Add QueueChannelOperations