AMQP-414: Rabbit annotation-driven endpoints

JIRA: https://jira.spring.io/browse/AMQP-414

This commit adds the support of Rabbit annotated endpoint. Can be
activated by both @EnableRabbit or <rabbit:annotation-driven/>
and detect methods of managed beans annotated with @RabbitListener,
either directly or through a meta-annotation.

Containers are created and managed under the cover by a registry
at application startup time. Container creation is delegated to a
RabbitListenerContainerFactory that is identified by the
containerFactory attribute of the RabbitListener annotation. Containers
can be retrieved from the registry using a custom id that can be
specified directly on the annotation.

The configuration can be fine-tuned by implementing the
RabbitListenerConfigurer interface which gives access to the registrar
used to register endpoints. This includes a programmatic registration
of endpoints in complement to the declarative approach. A default
RabbitListenerContainerFactory can also be specified to be used if no
containerFactory has been set on the annotation.

Annotated methods can have flexible method arguments that are similar
to what @MessageMapping provides. In particular, rabbit listener
endpoint methods can fully use the messaging abstraction, including
convenient header accessor. It is also possible to inject the raw
org.springframework.amqp.core.Message and the Channel for more
advanced use cases. The payload can be injected as long as the
conversion service is able to convert it from the original body. By
default, a DefaultMessageHandlerMethodFactory is used but it can be
configured further to support additional method arguments or to
customize conversion and validation support.

The return type of an annotated method can also be an instance of
Spring's Message abstraction. Instead of just converting the payload,
such response type allows to communicate standard and custom headers.

AmqpHeaders and DefaultAmqpHeaderMapper have been copied from
Spring integration. SimpleAmqpHeaderMapper is a reduced version of
the Spring integration counter part that does not support deprecated
fields and JSON specific constructs. Method hook points are available
so that a future version of Spring Integration can integrate those
customizations in an extension. Note that the default know maps all
user-defined headers so that the generated Message abstraction has
all the information stored in the protocol specific message.

MessagingMessageConverter is a new MessageConverter implementation
that produces a org.springframework.messaging.Message out of an AMQP
message and vice versa. AmqpMessageHeaderAccessor provides an easy
access of AMQP specific headers from a standard Message.

Issue: AMQP-414

AMQP-414: Polishing