INT-2269 Add ReplyChannelRegistry

Allows reply channel resolution after a message has been serialized
somewhere in a flow. Previously, the reply channel was lost.

With this change, the reply channel can be registered and the header
becomes a string (channel name) that can be serialized.

JIRA: https://jira.springsource.org/browse/INT-2269
INT-2269 Rename Registry to HeaderChannelRegistry

- Extract interface
- DefaultHeaderChannelRgistry
INT-2269 Polishing; PR Comments

- Add errorChannel registration as well.