INT-2831: Add Jackson 2 support

Add Jackson 2 support while retaining backward compatibility as much as possible.

Introduce a new abstraction for JSON conversion.

JIRA: https://jira.springsource.org/browse/INT-2831

INT-2831: Polishing

* remove `JsonObjectMapperFactoryBean`
* add @Deprecated constructors to `ObjectToJsonTransformer` and `JsonToObjectTransformer`

Polishing

Docs, compiler warnings.
Merge pull request #774 from artembilan/INT-2831

* INT-2831:
  INT-2831: Add Jackson 2 support
INT-2951 Add Context Id to Dispatcher has no Subs.

https://jira.springsource.org/browse/INT-2951

Provide the context id in the 'Dispatcher has no Subscribers'
message.

Ease debugging when more than one context in an application.

INT-2951 Polishing

PR Comments - add quotes to context Id in log message.

Polishing

INT-2951 Polishing

Change IOS to have a simple getApplicationContextId() and
add a method getFullChannelName() to AbstractMessageChannel.