si4demo Spring Integration 4.0 Demo

https://spring.io/blog/2014/05/15/webinar-replay-spring-integration-4-0-the-new-frontier
INTSAMPLES-122: Migrate to Gradle

JIRA: https://jira.springsource.org/browse/INTSAMPLES-122

INTSAMPLES-122: Polishing

INTSAMPLES-122: Add generated poms

* Upgrade some dependencies
INTSAMPLES-122: Cover Java/DSL sample