Add stomp-endpoint element parsing
Further updates to message broker xml config
Refactor XML websocket namespace

- websocket:handler-mappings is now websocket:handlers
- some external elements are now subelements

Issue: SPR-11063
Fix typo
WIP XML websocket namespace

- added bean definitions for messageConverter, messagingTemplate,
annotationMessageHandler
- register messageBroker (simple, noop or relay)
- refactor XML attribute names to lowercase and "-"

Issue: SPR-11063
Remove NoOpBroker - useless for XML configuration.
Register a UserDestinationMessageHandler and Polish
Add custom channels