INT-3139: add #jsonPath SpEL function support

* Add `<json-path-spel-function/>` component
* Add otional dependency on `com.jayway.jsonpath:json-path` artifact
* Add `JsonPathUtils` class as a wrapper around `JsonPath`
* Add `#jsonPath` tests for: `<transformer>`, `<filter>`, `<splitter>`, `<router>`

JIRA: https://jira.springsource.org/browse/INT-3139