The new UserDestinationMessageHandler resolves messages with
destinations prefixed with "/user/{username}" and resolves them into a
destination to which the user is currently subscribed by appending the
user session id.
For example a destination such as "/user/john/queue/trade-confirmation"
would resolve "/trade-confirmation/i9oqdfzo" assuming "i9oqdfzo" is the
user's session id.
Remove base class for STOMP-related message handler classes
(AbstractSimpMessageHandler), polish subclasses and fix issues with
more significant updates to STOMP broker relay.
Introduce base class for SubscribableChannel implementations providing
consistent logging for all channel implementations.
Rossen Stoyanchev