INTSAMPLES-137: Add WebSockets sample

JIRA: https://jira.spring.io/browse/INTSAMPLES-137

Depends on https://github.com/spring-projects/spring-integration/pull/1274

Polishing and cleanup

* Fix `cafe-dsl` project: https://build.spring.io/browse/INTSAMPLES-NIGHTLY-JOB1-1131
* Change author emails to the `pivotal.io`
* Regenerate poms

Fix for `Cafe-DSL` sample

https://build.spring.io/browse/INTSAMPLES-NIGHTLY-JOB1-1143