INT-2755: Support 'id' For <chain> Child Elements

* Introduce XSD 'id' attribute for all `<chain>` sub-components
* Register `<chain>` sub-components as Beans with names based on `<chain>` 'id'
* Generate aliases for sub-components based on element 'id'
* Add `<chain>` parser test to check sub-components as Beans within `BeanFactory`
* Ignore `NestedChainParserTests` as abnormal and confused for SI-configs
* Now `<chain>` sub-components are trackable by `MessageHistory`
* Now `<chain>` sub-components are eligible for JMX export
* Polishing some failed tests

https://jira.springsource.org/browse/INT-2755
https://jira.springsource.org/browse/INT-2321

INT-2755: Register as Beans only if 'id' provided

INT-2755: Set 'componentName' for handlers with 'id'

When components within `<chain>` are configured with an 'id' attribute
the 'componentName' of the handler is  constructed as:
chainHandler.componentName + '.' + handler.componentName.
Otherwise it is as was before.

INT-2755: Polishing

INT-2755: changes according PR's comments

* Add INFO about preference of `id` attribute for `<chain>` in the `ChainParser`
* Change `<chain>`'s sub-components `id` generation algorithm
* Configure `<chain>`'s sub-component `componentName` in the `ChainParser` instead of in the `MessageHandlerChain`
* Add `componentName` property to the `JpaOutboundGatewayFactoryBean`
* Add a note to the Reference Manual

INT-2755: Localize duplicate 'id' within chain

INT-2755: remove child beans aliasing

* Polishing tests
* Polishing docs

INT-2755 Polishing: Handle Nested Chain Bean Names

Previously named beans within a nested chain did not get unique
bean names.

INT-2755: Polishing nested chains

Doc Polishing
Merge pull request #753 from srt/INT-2755

* INT-2755:
  INT-2755: Support 'id' For <chain> Child Elements