INT-2455: HTTP outbound 'encode-uri' flag support

Now `<http:outbound-channel-adapter>` and `<http:outbound-gateway>` provide
`encode-uri="false"` option do not encode request uri.
It can be useful in some scenarios with non standard URL, e.g. RabbitMQ REST API:
'http://foo.RabbitMQ.com/api/queues/%2f/bar.queue'

https://jira.springsource.org/browse/INT-2455