INT-1362: #request SpEL function support

* Add `RequestAttributesUtils` to encapsulate #request SpEL function logic
* Introduce @GlobalConfiguration
to separate beans registration responsibility by modules
* Add 'component scan' for Integration `@Configuration` classes
* Optimize classpath scan by provided packages list to scan
* Add JavaDocs for new classes

JIRA: https://jira.springsource.org/browse/INT-1362, https://jira.springsource.org/browse/INT-2469