INT-3485: Remove final from `AE.stop(Runnable)`

JIRA: https://jira.spring.io/browse/INT-3485

Delegate to doStop() instead of overriding stop() directly

Delegated call to doStop() rather than stop(), added author tag and added unit test for custom doStop(runnable)

Polishing
INT-3479 Improve ServiceActivatingHandler.toString

JIRA: https://jira.spring.io/browse/INT-3479

- Remove null `beanName` in `AbstractStandardMessageHandlerFactoryBean`
- Change `ServiceActivatingHandler.toString()`
- Fix aggregator test timing