INTS-137: Add STOMP Chat application

JIRA: https://jira.spring.io/browse/INTSAMPLES-137

* Upgrade to Boot 1.1.7
* Fix several Boot apps to get deal with `args`, e.g. `--debug` option can be useful for Boot
* Provide a loca copy for JavaScript files (`sock.js` and `stomp.js`) to avoid extra Internet connection on testing

**DO NOT MERGE YET**
Depends on https://github.com/spring-projects/spring-integration/pull/1295