INT-3504: Deprecate `AmqpHeaders`

JIRA: https://jira.spring.io/browse/INT-3504

* Deprecate `AmqpHeaders` and extend it from `org.springframework.amqp.support.AmqpHeaders` for backward compatibility
* Change AMQP dependency to `1.4.0`
* Remove usage of deprecated `spring_reply_correlation` and `spring_reply_to` AMQP headers
* Fix syslog `DefaultMessageConverter` JavaDoc

Reformat code