INT-3527: Provide some useful changes

JIRA: https://jira.spring.io/browse/INT-3527

* `WebSocketInboundChannelAdapter` now handles `CONNECT` STOMP message and sends `CONNECT_ACK` message to the `WebSocketSession` immediately
* `ExpressionMessageProducerSupport` implementations now check the result of `expression` and if it is a `Message<?>` it is sent to channel without creating a new one
which has wrapped that `Message<?>` to the `payload` before
* Add `<script>` support to the `<outbound-channel-adapter>`
* Upgrade to the SF 4.1.1
* Add appropriate notes to the Docs