INTEXT-113: Make `.route()` as non-last component

JIRA: https://jira.spring.io/browse/INTEXT-113

Previously `router` could be configured only as last component in the `IntegrationFlow` definition.

* Remove `defaultOutputChannel` options from `AbstractRouterSpec`
* Populate `outputChannel` to the `AbstractMessageRouter.defaultOutputChannel`, when there is more EIP-methods after `.route()`
* Rename EIP-method `.recipientListRoute()` to the `.routeToRecipients()`
* Make compatibility with SI 4.1
* Tested against SF 4.1