INT-3434: AMQP Don't Declare Queue if Supplied

JIRA: https://jira.spring.io/browse/INT-3434

Previously `PointToPointSubscribableAmqpChannel` declared Queue always.
Change the logic to use `admin.declareQueue` only if `queueName` isn't specified.
In addition it is redundant to get deal with entire `Queue` object - just use the `queueName` for the `SimpleMessageListenerContainer`

Polishing

Declare queue the old way if not already present in broker,
even if the name is supplied.
INT-651: Add `Iterator` support for `Splitter`

JIRA: https://jira.spring.io/browse/INT-651
INT-651: Polishing according PR comments