Add SubProtocolHandler to encapsulate the logic for using a
sub-protocol.

A SubProtocolWebSocketHandler is also provided to
delegate to the appropriate SubProtocolHandler based on the
negotiated sub-protocol value at handshake.

StompSubProtocolHandler provides handling for STOMP messages.

Issue: SPR-10786

SI's BeanFactoryChannelResolver was BeanFactoryAware. This commit
brings Spring's BeanFactoryMessageChannelDestinationResolver in line
with the old SI class.

The resolver for /user/{username} prefixed destinations is now
more explicitly designed to store queue suffixes rather than session
id's, which is what we happen to use as queue suffixes.

This allows something other than the sessionId to be used without
having to change many places. It also enables applications to
construct destinations with user-specific queue suffixes without
making assumptions about what's used for queue suffixes. For
example a controller may construct a map with subscription destinations
and send that down to the client.

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.

Consolidates new, messaging-related classes from spring-context and
spring-websocket into one module.