Basic STOMP Server (SI)

Core STOMP infrastructure is in o.s.stomp and has no SI dependencies.

Currently, it only supports CONNECT, SUBSCRIBE, UNSUBSCRIBE, DISCONNET.

There's an abstract SI StompSubscriptionMessageProducer and a test
TestStompSubscriptionMessageProducer that emits 'Hello, world!' every
n milliseconds to open subscriptions.

This is configured into a test case StompOverWebSocketTests which
configures the message producer to send to its subscriptions every
2 seconds.

Run StompOverWebSocketTests and open stomp.html in a websocket-capable
browser (tested with Chrome on linux).

Currently the SI message payload is a StompMessage (headers and payload)
but there *is* a pair of STOMP transformers.