INT-2831: Add Jackson 2 support

* Introduce `JsonSerializer` strategy
* Change `ObjectToJsonTransformer` and `JsonToObjectTransformer` to use `JsonSerializer`
* Add `JacksonMapperJsonSerializer` and `Jackson2MapperJsonSerializer` implementations
* Change the `object-mapper` attribute to the `json-serializer`
* Introduce `JacksonMapperJsonSerializerProvider` factory to provide
`JacksonMapperJsonSerializer` or `Jackson2MapperJsonSerializer` instances dependently of the classpath

JIRA: https://jira.springsource.org/browse/INT-2831