INT-3312: Add Support for `outputChannelName`

JIRA: https://jira.springsource.org/browse/INT-3312

* Add `setOutputChannelName` to `AbstractReplyProducingMessageHandler` and `SourcePollingChannelAdapterFactoryBean`
to allow to have 'late binding' and resolve the real channel from `AC` on component initialization, instead of creation phase
* Add `setRequestChannelName` and `setReplyChannelName` to `ContentEnricher` for the same purpose
* Make `HeaderValueMessageProcessor` implementation `public`. It is useful for JavaConfig and DSL
* Polishing parsers to use classes, not their names as strings

INT-3312: PR comments

INT-3312: Polishing