INT-3511: Document WebSocket Support

JIRA: https://jira.spring.io/browse/INT-3511

Add note about Broker destinations

Doc Polishing

INT-3511: Fix 'useBroker' Docs and provide compatibility with SF 4.1.1
INT-3524 Fix Tooling MessageChannel References

JIRA: https://jira.spring.io/browse/INT-3524

A number of references (expected-type) still referred to
the Spring Integration 3.0 MessageChanel.