Fix ListenableFuture Docs

s/Thread/String/
INT-3500: Consider to add "error-channel" to the <enricher>

JIRA: https://jira.spring.io/browse/INT-3500

* add 'error-channel' to the <enricher> component
* delegate errorChannel to the internal gateway in ContentEnricher
* added tests for xml based and java based enrichers with error channels

INT-3500: Consider to add "error-channel" to the <enricher>

* Fixed typos and comments
* Reworked xml integration test to use the outputChannel and increased timeout
* Added overview in whats-new doc

INT-3500: Consider to add "error-channel" to the <enricher>

* Ensure requestChannel is set if an errorChannel is set
* Increased timeout to fix unit test
* Added details to content-enricher ref doc

Polishing
INT-3518: Upgrade versions and some cleanup

JIRA: https://jira.spring.io/browse/INT-3518
INT-3515: Fix Some WebSockets Issues

JIRA: https://jira.spring.io/browse/INT-3515

Change test suite to the Tomcat according IO

INT-3515: IllegalStateException for the `WebSocketInboundChannelAdapter`, when `useBroker = true`, but there is no Broker Relay in the Context
INT-3522: MQTT XSD: Fix client-factory attr type

JIRA: https://jira.spring.io/browse/INT-3522
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.
INT-3526 Used Expanded URI In Exception Message

JIRA: https://jira.spring.io/browse/INT-3526

Previously, the URI in the exception message is the raw
URI with placeholders, if present.

Use the expanded URI in the message instead.
INT-3512: Add `<advice-chain>` to the Aggregator

JIRA: https://jira.spring.io/browse/INT-3512
INT-3512: Fix typos
INT-3512: add `expire-` prefix to the advice sub-elements