Add Echo sample client [SWS-41]

**[Arjen Poutsma](https://jira.spring.io/secure/ViewProfile.jspa?name=arjen.poutsma)** opened **[SWS-41](https://jira.spring.io/browse/SWS-41?redirect=false)** and commented

Add the attached Echo client to the samples.


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**Attachments:**
- [EchoClient.java](https://jira.spring.io/secure/attachment/11770/EchoClient.java) (_3.55 kB_)
