Closes #2475

The message has to be sent after the endpoint starts up, which only
happens after the first request is accepted, so we put that logic
in the response extractor.

Signed-off-by: Gregor Zurowski <gregor@zurowski.org>

This allows clients to send batched up events in the same format as
before (or to continue to send single events). We can switch the
default format to an array in 1.4.x.

Fixes gh-1205

Fixes gh-873

For compatiblity with Angel streams we only need to set the content
type explicitly.

Fixes gh-873

Move turbine/hystrix amqp specific implementations to spring-cloud-stream based implementations and let the user decide which broker to use.

fixes gh-545