INT-3297: Add `@MessagingGateway` Support

JIRA: https://jira.springsource.org/browse/INT-3297

* Add `<gateway>` annotation analogue and its `MessagingGatewayRegistrar` to register `GatewayProxyFactoryBean` based on annotation attributes
* Add `@IntegrationComponentScan` and its `IntegrationComponentsRegistrar` to scan packages for integration components
* Add implementation to scan `@MessagingGateway`
* Add simple `@MessagingGateway` test

INT-3297: Further improvement

* Make `GatewayParser` to delegate the hard work to the `MessagingGatewayRegistrar`
* Add Docs
* Checked all existing tests

INT-3297: Polishing

INT-3297: Get rid of annotation dep from GWParser

Polishing - Docs and Assertion

Assert that the `@MessagingGateway` is on an interface.
INT-1834: Register Beans for Annotated Handlers

JIRA: https://jira.springsource.org/browse/INT-1834

The general issue has been raised about `MessageHistory` for annotated endpoints (`@ServiceActivator`, `@Transformer` etc.)

* Register generated `MessageHandler`s as beans with concrete names based on component, method and annotation.
* Add tests and docs

In addition revert the version for JRuby to 1.7.8 as other latests versions have a NPE issue around `System.console()`

Doc Polishing
INT-3294 Support Implicit Input Channel with Ann.

JIRA: https://jira.springsource.org/browse/INT-3294

Previously, implicit input channel creation was not
supported for annotated endpoints.

Register a `DirectChannel` if the input channel does
not exist in the context.
INT-3299 Remove Unneeded Dependency From IP

JIRA: https://jira.springsource.org/browse/INT-3299

The IP module incorrectly has s-i-stream as a transitive dependency.

It is only used in a test case.
INT-3404 Clarify Router Attributes

JIRA: https://jira.springsource.org/browse/INT-3304

Add notes to explain the relationship between `resolution-required`
and `default-output-channel`.